Vanity is the quality of being vain, or having a ridiculous amount of pride. If you have excessive vanity in your appearance, you probably spend long hours sitting at your vanity table doing your makeup or plucking your nose hairs.
If you pride yourself on looking absolutely perfect and refuse to do any work that might dirty your clothes or mess up your hair, someone might accuse you of vanity. Often vanity is empty, like the emperor’s in The Emperor's New Clothes. If someone pays to have her own book published even though it’s really bad, we say it is a vanity printing.