A 19th century term for a prostitute or a woman of questionable virtue. The implication is that the woman's skirt weighs very little and that it can easily be lifted up to engage in sexual intercourse.
Person A: Don't you bring your lightskirt here! This is arespectable house!
Person B: I beg your pardon! My fiancee is a proper young lady.
Lightskin activity usually refers to actions that enforce stereotypes about African American men with light skin. This includes constantly proving to the world that you're pretty, homewrecking, and being an overall menace to society.