A clear title is one that is free from anything that might encumber a person's legal claim to ownership. If you buy a piece of real estate, then the title should be transferred to you, but it's important to do some research to ensure it's a clear title. If the title isn't clear, then you could face an ownership dispute because of a past matter you had nothing to do with.
Other terms for a clear title include "good title," "clean title" and "free and clear title." Usually, these terms mean that the person or entity holding the title has a free, clear right to ownership and that one can transfer all ownership rights to the property in a sales transaction.