Frames were a knowledge representation format proposed by Marvin Minsky in his 1974 paper "A Framework for Representing Knowledge" [L1 ].
Briefly, a frame has a name and a set of attribute-value pairs (known as slots). These slots can be filled by data, methods, or (references to) other frames, and can have event listeners attached to them (much like variables in Tcl's namespaces).
While the concept was quite popular originally, it seems to have lost out to Semantic Networks and, particularly, Object Oriented Programming. Prototype-based OO (as in Self [L2 ]) seems to come quite close to frames.
Chris Fugate developed an implementation of frames for Tcl which was available from [L3 ] although this site seems to be defunct (as of 30 Dec 2005). See this comp.lang.tcl discussion: [L4 ]
Frame systems seem to still have some popularity in the knowledge representation community, and the Semantic Web efforts. For instance, the Protégé ontology editor [L5 ] uses a frame system by default (although it can also use OWL).