Warranty Deed
  
See: Warranty.
A warranty deed is a fancy sounding term for a concept that seems almost "no duh" when it gets explained. It has to do with providing assurances of clear title before selling a property. But, because lawyers need to do lawyerly things, we end up with a term like "warranty deed."
So...you own a property and you're going to sign over the title to someone else. The warranty deed says that you own the property free of all liens and encumbrances, and that you have the right to transfer it.
That's it. It basically just shows that you own it, no one else has a say in what you do with it, and you have the right to transfer title.