Deeds are the legal document that simply transfers ownership or interest in a property from one entity to another. The quit claim deed is a way to transfer any interest a person or entity has in a property to another person or entity. The name is the easiest way to remember it, because they are essentially 'quitting' their claim to a properties ownership.
These differ from Warranty Deeds in that the person transferring ownership is not providing any guarantee of ownership, or that the title is clear or even capable of being transferred.
Quit claim deeds are useful when an entity is transferring ownership or just re-titling property, such as upon marriage, at divorce, to a personal trust, or from an individual into an L.L.C. or Corporation. They are also great ways to clear title defects, such as in the case of potential adverse possession situations.