the party TO an agreement

What do you formally call an entity or person who enters into an agreement?

the only correct version:

the party TO an agreement

– the party of the agreement
– the side of the agreement
– the part of the agreement

Note other possibile combinations:

1. the party to a/the dispute

2. the party to negotiations

3. the party to trade talks

4. the party to a/the treaty

5. the party to a/the settlement