This option sets the limit on the number of simultaneous requests that will be served. When PHP scripts for this domain are set up to run via FPM, this controls the maximum number of child processes. When the `pm` option is set to `static`, this is the number of child processes that will be created. When the `pm` option is set to `dynamic`, this is the maximum number of child processes that could potentially be created.

Based on the PHP-FPM workload profile selected in Virtualmin Configuration, a recommended value is calculated using available system memory.

When PHP scripts for this domain are set up to run via FCGI, PHP child process management should always be disabled, which will only route one request at a time to application processes it has spawned. By default, and with the environment variable setting `PHP_FCGI_CHILDREN=0`, PHP child process management is disabled.