Prolix means "Using or containing too many words." In other words, being extremely lengthy, or verbose. It means to use an insane amount of words to explain a word, concept, idea, or other such thing. You normally wouldn't need that many words, but you use more than necessary, hence prolix. If a description of anything, such as a word, contains several sentences merely repeating themselves repetitively and being really redundant, than you can call that description a "prolix description." Like this one for instance.