The difference between a read lock and a write lock

A shared lock (S lock) is also called a read lock, and if the transaction T is a plus s lock on the data object A, the transaction T can read a but cannot modify a, and the other transaction can only have a plus s lock, not the x lock, until T releases the S lock on a. This ensures that other transactions can read a, but cannot make any modifications to a before T releases the S lock on a.
An exclusive lock (x Lock) is also called a write lock. If the transaction t has an X lock on the data object A, the transaction T can read a or modify a, and the other transaction cannot add any locks to a, until T releases the lock on A. This ensures that the other transaction cannot read and modify a until the lock on the A is released by T.

The difference between a read lock and a write lock