A web server is a computer containing software for, and connected to infrastructure for, hosting, or serving, web sites written in HTML. The most common web server software on the internet is Apache, which is frequently used in conjunction with PHP, Perl, and other scripting languages.

It is possible to create one's own web server, hosted on any speed of internet connection, but many people choose to purchase packages from hosting providers, who have the capacity and facilities to provide adequate bandwidth, uptime, hardware, and maintenance for frequently-visited web sites.

Reference http://codex.wordpress.org/Glossary