Below mentioned is an introduction to hooks and its type:
Hooks allows your plugins to ‘hook into’ the WordPress and perform certain tasks and actions. It is used to call functions in plugins at specific times, and thereby set plugins in motion. There are two types of hooks in WordPress Blog:
Hooks that the WordPress launches at specific points during execution, or special for a specific event occur. Plugins can specify that its PHP functions are executed at these points, using the Action API.
Hooks that WordPress launches to alter any text of various types in WordPress before adding it to the database or sending it to the browser screen. Plugins can specify that its PHP functions is executed to alter specific types of text at these times, using the Filter API.