It is fitting that the word "frame" has multiple obsolete definitions, according to the Oxford English Dictionary (everything from "warlike array" to "established order of government"). Even the variations of the noun form that are still operative range from cognitive structures to elements of home-building. The general definition of "a set of standards, beliefs, or assumptions governing perceptual or logical evaluation or social behaviour" is useful in that it comprises elements of infrastructure and mediation. (see code) This definition leads to the inherent paradox of defining the term "frame": the signifier encompasses not only the content of an object but also the organizing structure. The frame can be read as a self-contained semiotic element as well as a catalyst of semiological inquiry, identifying crucial debates within the designated content, and establishing the vocabulary common to the independent system in question. This is the precise duality which will inform much of the "framing" of art and media.
From this brief overview of etymological history, the theoretical and ideological implications come clear. A frame or framework can never be purely abstract, though, and an understanding of its ideology is contingent on an exploration of its role as a physical marker. A frame is firstly an element of materiality in physical bodies that can act as mediums (i.e., a canvas or a building). This could be considered the architectural or physical permutation of the term, applicable to things manmade and biological. For, according to the OED, a frame is also "a structure which serves as an underlying support or skeleton, or of which the parts form an outline or skeleton not filled in." Although this definition refers, in context, to living bodies, it can be extended to any structure with a similar support system; the important element is the presupposition that a physical frame connotes something "not filled in." There is an element of lack here; a frame is somehow "the beginning" of something, but its meaning is either absent or inchoate, requiring body and substance to complete it. The most common and recognizable manifestation of this in the inanimate world is the window, complete only with frame and pane of glass.
The analogy of the windowpane reveals the role of a frame as the marker of a place where a medium (and/or a message) can operate, and therefore constitutes a transition from the composition of the frame and its filler to the manifestations of their interrelationship. In his Questions of Cinema , Stephen Heath purports that "the pane is at once a frame, the frame of a window, and a screen, the area of projection on which what is seen can be traced and fixed." (Heath 34) [see screen, (2)] The frame fulfills Heidegger's idea of a clearing, a blank space where the artist can extend his own body and mind onto a two-dimensional surface  . The art of framing itself has historically had a rich and influential role in artistic and curatorial endeavors. The physical frame was a late development in art, gaining popularity during and after the Renaissance in Europe. While not only signifying the piece as a luxury item, in the case of gilt framing, the easel and frame are certainly influential over the act of image-reading. It mediates the spectatorship experience, "enclosing and focusing the viewer's gaze onto the scene which unfolds within its boundaries. Such a device places the frame within the space of the viewer and marks the point where 'real space' ends and represented space begins." (Carter 73) [see reality/hyperreality, (2)] This evolution makes it clear that the frame can be an actual material part of an artwork, and therefore should be foregrounded as content, under Clement Greenberg's definition of the avant garde .
The very existence of a frame reinforces the skewed and weighted perspective that comes from choices in composition. The act of framing can signify that what is on the canvas is somehow to be distinguished from or elevated above what is exterior to it (and therefore deemed inadmissible by the artist). "The convention of constructing frames out of precious materials clearly signals the image as being a precious object, but it can also signify depictive intensity, the place where something special or extraordinary is taking place." (Carter 74-75) Of course, not all frames are made of precious metals; contemporary fashions in framing also attempt to mark the work by either eliminating the frame, reducing its visibility, or adopting materials that carry other associations (i.e., wood, stainless steel).
The physical frame is made more semiotically potent once combined with knowledge of cognitive organization. Michael Carter traces the "history" of the abstract frame or border in his Framing Art:
We have an expectation that two-dimensional images will be bounded by a fixed edge (margin) and in many instances a frame as well...The horizontal base line appears first and doubles up as the bottom of the image and as a grounding line which acts as a support for the figurative elements...It was only later that the vertical margins of the field became pronounced and joined up with the horizontal margins to form 'an homogenous enclosure like a city wall'. (Carter 73)
The distinction here of an "enclosure" or "wall" has implications of restriction and containment that often accompany the application or extraction of a frame. The necessity for boundaries in any distinct image implies a corollary necessity of choice, and therefore of omission. The presence of a boundary or frontier-like edge broadcasts "representation," and urges the viewer to read this area of space under a different set of rules from the external, or "real" space. Carter concurs: "one of the fundamental characteristics of a visual image is that it has an edge, that it stops. Unlike 'reality' which appears as unbounded, the image constantly displays to its viewer the fact that it is different from 'reality' by having an edge." (Carter 149) The frame provides stability, a mediatory process that encodes the space in which the object is placed.
The frame then provides a space for signification by establishing a hegemonic relationship between the viewer and the represented. Heath references Saussure's linguistic sign in terms of the movie screen: "the frame is the reconstitution of the scene of the signifier, of the symbolic, into that of the signified, the passage through the image from other scene to seen." (Heath 12) The space within the frame signifies the represented world and provides a means of coping with the outside world and its continual perceptive shifts. (see symbolic ) It is in this space that one can abstract the term "frame" from its entrenchment in the physical definition detailed above and return to the OED's notion of the term as an interpretive framework. Frame analysis has been a key theory in cognitive studies, especially in attempts to understand how subjects mediate the overwhelming amount of stimuli present in the world. The mapping of a frame onto an idea, whether as a (dis)continuous border or an endoskeleton, assists in establishing boundaries, connections, and internal systemic elements. Erving Goffman's Frame Analysis provides useful examples of ways that humans organize experience according to certain principles; he labels each identifiable element of this organization a "frame." "Whatever the degree of organization, however, each primary framework allows its user to locate, perceive, identify, and label a seemingly infinite number of concrete occurrences defined in its terms." (21) The plurality of possibilities under the rubric of what I've taken to calling the "filler" speaks to the utility and flexibility of even the simplest of frameworks . Goffman discusses at length the use of frame narratives (and breaks in those narratives) in prose, drama, and music. Although the examples and permutations of frame activity are infinite, it is important to recognize that framing content in these media becomes a question of genre; when structure and content perform this interplay, the structure of the medium (to bastardize Marshall McLuhan) does indeed become its message. 
The term frame is probably most closely associated, in modernity, with the motion picture. The lexicon of film terms expresses the persistent duality of the term: "frame" can refer to either the substance of an individual shot or the border of the screen that contains a certain image. In his Complete Film Dictionary , Ira Konigsberg presents these two opposing yet harmonious definitions: "The borders of the image on the screen [see screen , (2) ] that enclose the picture like a frame on a painting" or "The entire rectangular area of the image projected on the screen." (Konigsberg 156) However, even these possible meanings are still technical or spatial, describing elements of the screen that are presented to the audience (with the possibility of variables like size or speed). When the role of the director is considered, the questions of choice, inclusion, and elimination inform the process much like the frame narratives detailed in Goffman.  The images here, of course, are moving, one right after another in succession. This movement can somewhat obscure the inherent fact that directors are guiding audience reception, focusing on certain portions or elements of the self-contained illusion of motion. The viewer is kept watching, moving his/her eyes over various portions of the space, which the director has carefully composed to seem like its own world. Konigsberg posits that the frames, though indistinguishable one by one, can be read and synthesized like words, left to right. "The center of the frame is normally the place for important action, while the rest of the frame must be so arranged that it does not draw attention unless to comment on the major action." (Konigsberg 156) Even the existence of the frame dictates a normativity of composition and viewership.
In fact, the frame as a semiotic element is so important in film theory, that the term "mise-en-scene" has been coined to refer to the visual composition of individual shots. This includes camera position and angle; setting; costume and lighting; and the relation of people, objects, and movement within the compositional frame. It is an "extracinematic" code that is not unique to cinema: it was adopted from theatre, where it referred to staging. The ramifications of framing not only extend to theater but most likely originated there, with the proscenium stage "framing" the action. Even sculpture, probably the least easily bounded art form, as it essentially is its own frame, shows a history of spatial indicators that guide or direct spectatorship. Martin Heidegger points out the importance of space in this right: "Sculptured structures are bodies...The forming of it happens by demarcation as setting up an inclosing and excluding border. Herewith, space comes into play." (Heidegger 3) The persistence and omnipresence of frames in visual media supports what WJT Mitchell would refer to as a "metapicture," that is, the inevitable impossibility of ever getting outside a picture. Although pictures within pictures "can, in principle, keep [their] levels, boundaries, and frames distinct," there is a world where there is nothing outside the picture. In this case, if the theory holds water, the frame becomes essential (showing the transgression of limits) and moot (if everything is in the image, then there is seemingly no frame at all). Boundaries can be ambiguous, disputable, or unapparent; however, there would be no notion of inside or outside if it weren't for the concept of framing in the first place.