A condition variable is a synchronization primitive used in programming to manage the execution of threads. It allows threads to wait for certain conditions to be met before continuing their execution. This is particularly useful in scenarios where one thread needs to wait for another thread to complete a task or update a shared resource. Condition variables work in conjunction with mutexes, which are used to protect shared data. When a thread finds that a condition is not met, it can wait on a condition variable, releasing the associated mutex. Once another thread changes the condition and signals the condition variable, the waiting thread can wake up and recheck the condition before proceeding.