Actions
Event triggers. Hooks that fire at specific times during WP execution to run your custom code.
do_action() add_action()
240+ hooks Filters
Data modifiers. Hooks that allow you to intercept and modify data before it is saved or rendered.
apply_filters() add_filter()
129+ hooks Functions
The standard library. PHP functions available in the global namespace.
get_post() wp_remote_get()
4125+ functions Classes
Object-oriented Core. The fundamental classes that power the Loop, Users, and Roles.
WP_Query WP_Error
640+ classes