In geocaching, a muggle is a term used to refer to someone who is not a geocacher. The term was adopted from the Harry Potter series of books, where it was used to describe someone who is not a wizard. Muggles are usually unaware of the game and know nothing about it. When geocachers advise others to be wary of muggles, it simply means to be cautious of non-geocachers who may accidentally discover a cache or interfere with the game.