Types of Locks in Database

Locks in database (Definition taken from Wikipedia):

A lock, as a read lock or write lock, is used when multiple users need to access a database concurrently. This prevents data from being corrupted or invalidated when multiple users try to read while others write to the database. Any single user can only modify those database records (that is, items in the database) to which they have applied a lock that gives them exclusive access to the record until the lock is released. Locking not only provides exclusivity to writes but also prevents (or controls) reading of unfinished modifications (AKA uncommitted data).

A read lock can be used to prevent other users from reading a record (or page) which is being updated, so that others will not act upon soon-to-be-outdated information.

Types of Locks in Database:

Shared Locks: Used for operations that do not change or update data (read-only operations), such as a SELECT statement. 
 
Update Locks: Used on resources that can be updated. It prevents a common form of deadlock that occurs when multiple sessions are reading, locking, and potentially updating resources later. 
 
Exclusive Locks: Used for data-modification operations, such as INSERT, UPDATE, or DELETE. It ensures that multiple updates cannot be made to the same resource at the same time. 
 
Intent Locks: Used to establish a lock hierarchy. The types of intent locks are as follows: intent shared (IS), intent exclusive (IX), and shared with intent exclusive (SIX). 
 
Schema Locks: Used when an operation dependent on the schema of a table is executing. The types of schema locks are schema modification (Sch-M) and schema stability (Sch-S). 
 
Bulk Update Locks: Used when bulk-copying data into a table and the TAB LOCK hint is specified.