SDL_Condition.3type - Man Page

#include <SDL3/SDL_mutex.h>

typedef struct SDL_Condition SDL_Condition;

Condition variables, paired with an SDL_Mutex, let an app halt multiple threads until a condition has occurred, at which time the app can release one or all waiting threads.

Wikipedia has a thorough explanation of the concept:

https://en.wikipedia.org/wiki/Condition_variable

This struct is available since SDL 3.2.0.