An object is any item that is inanimate. For example, an armchair is an object, as it is inanimate; it does not breathe, eat or think. A human, however, is technically not an object, as it is living, it breathes, it eats and it thinks.
For a more detailed treatment, see Subject and predicate.
In grammar, an object is a noun or pronoun appearing in the predicate of a sentence.