Other forms: lasses
A lass is a girl. Your Scottish folk dance teacher might announce, "Lads line up on that side, lasses on this side!"
Lass is an old-fashioned way to say "young girl," and it's more common in parts of Britain than in the US. You're most likely to hear this word in Scotland and the north of England, although lass is most likely rooted in Scandinavian languages, like the Old Swedish løsk kona, "unmarried woman," or the Old Norse löskr, "idle or weak."