Common underwear types:

• boxers_(clothing) - Boxer shorts; a type of underwear distinguished by their long, shorts-like style. They may look very similar to shorts, but are typically used as an undergarment. Not to be confused with boxer briefs. Boxer briefs have a firm fit while boxer shorts are much looser.
• boxer_briefs - A hybrid underwear that combines the features of boxers and briefs. This type of undergarment is characterized by its medium-sized length in the leg and by its relative tightness.
• briefs - A type of legless, tight underwear. On e621, the tag refers to the style traditionally worn by males, and not, for example, women's briefs. Some briefs have a two-part front with an opening designed to slip the penis through for quick urination (as opposed to pulling it over the top).
• jockstrap - A type of underwear designed to support the male genitalia, traditionally used during sports. Typically consists of a waistband with a front pouch containing the penis and balls, and two connecting straps in the back which leave the butt exposed.
• fundoshi - A traditional Japanese underwear that is much like a loincloth. It is often a single piece of cotton cloth, covering the crotch and twisted and tied up like a thong at the back.
• panties - Article of clothing usually (but not always) found on females. Panties are typically made of thin cloth, which with being skin tight makes them nearly invisible through clothing on top of them. They are narrow at the sides and have a triangularish form in front and at the back.
• thong - Underwear that consists of a thin piece of material that goes around the waist and rides up along the butt crack (in a bare-all fashion, keeping cheeks mostly exposed) looping under and over the genitals, which are covered (most times) by another patch of material. Often sported as [lingerie] or as swimwear (bikini thong). Not to be confused with flip flops or sandals.