Shared hosting is the most popular type of web hosting. It's what people usually mean when they talk about "web hosting". Shared simply means that many websites, from multiple customers, reside on a single web server, so the server resources (Processor, RAM, Disk Space) are shared among them.
The main benefit of shared hosting are very cheap prices. Since hundreds of websites are hosted on the same server, instead of costing hundreds of dollars per month (which would be a monthly price for a whole server), most shared hosting plans are just $5-$10 per month.
Ease of use
All shared hosts include a web control panel so it's very easy to setup and use. You can easily add a new website, design it using their included web builder (just by dragging and dropping the elements you want), or you can use their one click installs to install blogs, forums, photo galleries, online stores and other software. If you want something even easier to use than shared hosting check out managed hosting.
What kinds of website it is for?
Shared hosting is the best for small to medium websites. It's great for your first website, since it's very easy to setup and build a real website, for a small business website and pretty much all kinds of simple websites up to a million monthly visitors. Even if you plan to grow your website in the future there's no need to start paying $100+/month right away for a dedicated server, you can always transfer to a more expensive hosting later on.
Popular shared hosting providers:
iPage (founded 1998, hosting over 1 million websites)
FatCow (founded 1998, hosting over 500,000 websites)
HostGator (founded 1998, hosting over 2 million websites)