An undershirt in American English (vest in British and South African English, banyan in the Indian Subcontinent, or singlet in Australia and New Zealand), is an article of underwear worn underneath a dress shirt so as to protect it from body sweat and odors.
More generally, the term refers to an upper-body garment worn next to the skin (innerwear) by men. It can have short sleeves (T-shirt) or be sleeveless (A-shirt).
An undershirt may be worn to protect the body from stiff or otherwise uncomfortable fabric. It also makes dress shirts less transparent, to reduce the amount of sweat absorbed by the shirt's fabric. It can be worn during winter months as an extra layer of warmth, and reduces wear on the upper layers of clothing.[1][2]