Lock-in refers to a written agreement guaranteeing a home buyer a specific interest rate on a home loan provided that the loan is closed within a certain period of time, such as 60 or 90 days. Often the agreement also specifies the number of points to be paid at closing.
Source: Federal Trade Commission
Since interest rates can change frequently, many lenders offer an interest rate lock-in that guarantees a specific interest rate if the loan is closed within a specific time.
Source: U.S. Department of Housing and Urban Development
The guaranty of a specific interest rate and/or points for a specific period of time. Some lenders will charge a fee for locking in an interest rate.
Source: Ginnie Mae