# Filters

[Filters](https://developer.wordpress.org/plugins/hooks/filters/) give you the ability to change data during the execution of WordPress Core, plugins, and themes. Callback functions for Filters will accept a variable, modify it, and return it. They are meant to work in an isolated manner, and should never have [side effects](https://en.wikipedia.org/wiki/Side_effect_\(computer_science\)) such as affecting global variables and output. Filters expect to have something returned back to them.
