SQL Server has 3 main lock types:

Shared: Locks are compatible with other shared and update locks.

Update: Locks are compatible with shared locks.

Exclusive: Locks are not compatible with any other locks.

Apart from lock types, there are transaction isolation levels for managing security among transactions:

READ UNCOMMITTED

READ COMMITTED

REPEATABLE READ

SERIALIZABLE

SQL Server has some locking optimizer hints along with lock types:

NOLOCK

HOLDLOCK

UPDLOCK

TABLOCK

PAGLOCK

TABLOCKX

READCOMMITTED

READUNCOMMITTED

REPEATABLEREAD

SERIALIZABLE

READPAST

ROWLOCK