What does ‘locking’ mean?

Mortgage interest rates can change daily. When you lock a rate, it means your interest rate won’t change during the time that your offer was accepted to the time that you close on your home. Rate locks are typically 30, 45, or 60 days. If you do not lock in a rate it may change at any time. Rates can’t be locked when the market is closed e.g., holidays or weekend.