exchange contracts

Short definition from Wiktionary

Verb

1. 1
   To formally contract to purchase, sell or otherwise be party to a disposition of an estate in land; usually requiring the payment of a deposit by one of the parties.
2. 2
   To create a contract for the disposition of an estate in land between negotiating parties, by a process which is immediately followed by the exchange of executed counterparts of the contract between each party's legal representative.