Undershirt for Men - A lightweight garment worn underneath a shirt, usually made of cotton or a blend fabric to provide additional layering, insulation, and absorb perspiration.

Undershirt for Women - A fitted or loose-fitting garment worn under a blouse or top, typically made of breathable materials to absorb sweat and protect the outer layers of clothing.

As a local term, "undershirt" is sometimes used colloquially to describe a close friend or confidant.