As used in philosophy, in general, an object is something that can have properties and relations. Hence a particular object is, basically, either a particular material body or a particular mind--or, on a neutral monist view, a particular that can be viewed under both physical and mental aspects.

Symbols represent objects; how they do so, the map-territory relation, is the basic problem of semantics.

Objects are often treated as types of particulars, but occasionally, philosophers see fit to speak of abstract objects--Platonic forms would be an example.

Much, much more at objecthood