Nginx is a free, open-source, high-performance HTTP web-server which unlike some other web-servers, it does not rely on threaded handling of the requests but instead it uses a much more scalable event driven (asynchronous) architecture.
This uses a very small and predictable amount of memory under heavy load. Nginx in combination with the simple and very robust FastCGI Process Manager for PHP (PHP-FPM) and the world most popular database server MySQL can give you a lot of power and performance while still using a small memory footprint.
The following article is all about how to install and configure LEMP Stack on a CentOS 6 VPS and host blazing fast WordPress powered web applications.