A mobile website is one that is optimized for viewing on a mobile phone. Websites that are not mobile-optimized are small and difficult to read, whereas mobile optimized sites have an interface suited for mobile phone navigation.
Given the proliferation of touch screen phones and tablets, many mobile websites support functionality for hand movements (as opposed to mouse clicking).
You’ll notice that many mobile websites have a different URL than a regular web page. One good example is YouTube. YouTube’s web page can be found @ www.youtube.com and mobile webpage @ m.youtube.com. Most URLs will automatically redirect you to a website / mobile website if you are browsing on your computer / mobile phone.
Browsers used to surf the mobile web are similar to browsers used for normal web browsing. Examples include Safari, Opera Mobile, Skyfire, Google Android, Microsoft IE for Mobile, Firefox Mobile and Bolt.
If you ever come across the term "WAP" (wireless application protocol), it's a three letter acronym that describes the standard used to build mobile websites.