Git hooks are executable scripts you can place in $GIT_DIR/hooks directory to trigger action at certain points. 

There are two groups of these hooks: client side and server side. 
The client-side hooks:
are for client operations such as committing and merging.
The server-side hooks:
are for Git server operations such as receiving pushed commits.

See Also [ http://git-scm.com/book/en/Customizing-Git-Git-Hooks ]