[Now, here's a challenge. Discuss what an "object" is, from a Tcl point of view!]
An object, from an object orientation point of view, might be thought of as an entity within an application which has executable code as well as related data and state.
It is, generally (always?) a specific instantiation of one or more classes.
See also Object (Computer science) [L1 ] at Wikipedia.
Other kinds of objects related to Tcl are: