Final answer:
The keyword to end Proc SQL is QUIT. It is used in SAS to exit the PROC SQL step after executing SQL statements and frees up resources.
Step-by-step explanation:
The keyword used to end Proc SQL is QUIT. In the SAS programming environment, when you are done executing SQL statements within a PROC SQL step, you use the QUIT statement to exit the procedure. Unlike a RUN statement which only signifies the end of the current SQL query, the QUIT statement completes the entire PROC SQL step and ensures that all results are displayed and that the required resources are freed up.