The setting up and running of a server to serve web pages via the Internet or LAN. Technical questions about the server (if you have access to it) maybe best asked on serverfault.com. Read the answers to this question: http://webmasters.stackexchange.com/questions/20838/how-to-find-web-hosting-that-meets-my-requirements before asking your hosting question. If you ask something that's already answered by that question it will probably be closed as duplicate
Web Hosting in simple terms is a service that stores your website on a server, allowing users to access it over Internet.