Shared hosting, sometimes called shared services or virtual hosting, is simply when multiple web sites share the same server, thus reducing the cost for everyone.
With a shared hosting account, your site will usually be on a server with hundreds of other web sites. That may sound like a lot, but it usually works out extremely well because most sites don't generate enough traffic or use enough resources for it to become a problem.
Share hosting is suitable for personal sites, small businesses, and even medium sized businesses if their hosting needs fit within the parameters of a small business.
Most shared hosting providers offer substantially more disk space, data transfer, and email accounts than most people or businesses need. If every site used their quota, shared hosting would not work. But since few do, it actually works out quite nicely.
Because most people and businesses don't use most of the features they have available to them, using feature lists to choose a web host doesn't usually narrow the field much. What should be the criteria used to choose a host is harder to measure, so most people end up making uneducated choices and hope for the best.