Also known as: 汗衫
A light typically collarless shirt or top made to be worn underneath other clothing, such as Dress Shirts. They're frequently plain and white.
Men may wear "wifebeater" Tank Top-style sleeveless undershirts, especially to accentuate a blue-collar look. For women, there may be some overlap with Camisole. They may be worn in lieu of a Bra by (typically younger) flat-chested girls with no need for supporting their breasts.
In terms of Sportswear, the term "undershirt" usually refers to a shirt worn under most clothing (a Baseball Uniform, for example).
This tag should not be used for Dress Shirts.