An acronym for "object-oriented". (or was that "object-obsessed ?-) RS
Tcl abounds in extensions providing an object orientation (OO) programming style - see that previous link to read about incr Tcl and the others. See Category Object Orientation for additional relevant hits.
Further, there are activities such as object-oriented analysis (OOA) and object-oriented design (OOD) that concern themselves with analyzing a system (or a solution to a problem) in terms of objects and their behaviors.