T cells have a single target, like antibodies. The target is a peptide, a fragment of a protein 8-11 residues long. That peptide could show up in several target proteins, but usually (?) is unique to one protein.

This is a bit of an oversimplification. Firstly, the peptide is 8-11 residues for cytotoxic, aka killer, T cells which i think is what we're talking about here. It's 13-17 residues for for helper T cells. Secondly, there are varieties of T cells which don't have a single target, like invariant natural killer T cells, but those are pretty obscure, and not what people are talking about when they just say "T cells".