The term "thicc-ass" is a slang expression used in adult content and is derived from the word "thick". In the context of porn video tags, it refers to a person's buttocks being notably larger or more voluptuous than average. It is often used as a compliment and can be seen as an indicator of physical attraction towards an individual with a curvy or prominent rear end. The term "thicc" has become increasingly popular in recent years as a playful way to describe a fuller, rounded, and appealing backside.