Allowed memory size exhausted

WordPress triggers a fatal error when a PHP script tries to use more memory than the limit defined for the process. The limit is set by the PHP memory_limit directive or by WordPress constants such as WP_MEMORY_LIMIT.

When the limit is reached, PHP stops execution and prints the error message. The condition occurs because the request loads large data structures, runs intensive plugins, or runs on a host that enforces a low memory cap.