Bottoms are an apparel term used to describe the layers of clothing worn on the bottom half of the body. Bottoms may be in reference to undergarments or outerwear.
About Underwear:
Underwear refers to any article of clothing designed to be worn under the clothes and close to the skin. Articles of underwear for women may include, but are not limited to; bras, sports bras, bikini briefs, boy shorts etc. Articles of underwear for men may include, but are not limited to; boxer briefs, briefs, cotton t-shirts, base layer pants, etc.