A knowledge base (or “knowledgebase”; abbreviated KB or kb) is a repository of articles for your users. It's a database of knowledge on a specific topic - in this case, support issues. Some knowledge bases have an artificial intelligence component. They suggest solutions based on feedback provided by the user, and can learn from experience.
FAQ's, or Frequently Asked Questions, is just that - FREQUENTLY asked questions with answers. A knowledge base is useful when the FAQ's don't have the level of detail for a user or their problem is not listed.
Knowledge base articles might have screen-shots, step-by-step instructions, or even video if warranted.
Knowledge bases are used via online helpdesk packages that allow users to search and retrieve the information.
If you want to use a knowledge base on your support web site, you must understand how to write the knowledge base articles correctly. You also need to know how to pick the right knowledge base software and configure it properly for your unique situation.