A very unattractive person who thinks they are the bomb when they really aren't. They usually have no teeth and hair talking bout "Yo whats your name" up in the club knowing they have no money to buy you a drink!
Semen that is pleasant to taste, easier to swallow, sweeter and less bitter than regular cum which is sour, most likely spit out, or used to lubricate other parts of the body. It can also be used to describe any one who looks tasty, sexy, attractive, edible, lick-able.
The difference between cum and yum really depends upon ones personal taste. She looked over seeing him for the first time, purred like a cat and said YUM!