While "consummation" is not defined by Oklahoma statute or case law, in the context of a contract, it is when the contract has been executed and the parties are obligated to perform, i.e., closing.
Although you didn't ask how this definition ties in with right of rescission, Title 15 O.S. Sec. 232 states: A contract is extinguished by its rescission. Thus you have a binding contract at closing (the bank must lend, and the borrower must pay under the note), but if the borrower rescinds, the contract is extinguished ("dead").