Executed agreements - performance of the agreement has been performed.

Partly executed agreements performance of the agreement has begun.

Executory agreements -neither side has performed any part of the agreement (their promises yet).

Why does the distinction of executed and executory agreements matter?

In the context of ‘uncertainty’ about the terms of an agreement:

The courts are reluctant to find that there is no contract once the agreement is partly executed (i.e. once performance has begun). Because, by beginning to perform the agreement the parties have shown the court that the agreement is workable in practice. And, it would be harsh to find that there is no enforceable contract where one party has already relied upon the agreement and partly performed their obligations