Shared web hosting is a service that lets you host your websites on a web server with a whole bunch of other web sites. Your web site shares the web server's hardware and software.
As long as your web site doesn't need all of the server's resources, this is the cheapest option for you because you are sharing the costs with many other people.
For hosting a heck of a lot of web sites, for one. You don't need to buy several hosting packages just to host multiple web sites so it makes hosting web sites very cheap. Shared web hosting also makes it really easy for you to administer your web sites.
The hosting company handles all of the complicated configuration, set-up, and maintenance. You just have to use their simple control panel to add domains, set up email accounts, review server logs, upload files, and install scripts. Popular control panel software include cPanel.