PHP-FPM stands for "PHP FastCGI Process Manager." It's an alternative to the traditional PHP module for web servers like Apache or Nginx. PHP-FPM provides a FastCGI interface for PHP scripts to be processed and managed more efficiently.

Unlike mod_php, where a separate PHP instance is started for each Apache child process request, PHP-FPM uses a central process manager that manages a pool of PHP processes. This allows for better resource utilization and scalability for web applications.

PHP-FPM also provides features such as process pool tuning, load balancing, and monitoring of PHP processes. It's particularly useful for websites or applications with high traffic volumes, as it improves performance and stability by optimizing resource usage and avoiding bottlenecks.