Boxer briefs (or tight boxers) are a type of men's undergarment which are long in the leg, like boxer shorts but tighter-fitting, like briefs; a hybrid between the two main types of male underwear in Australia, Canada, United Kingdom, and the United States. Depending on the manufacturer, boxer briefs may also be spelled as one word: boxerbriefs. They are sometimes called "trunks" in Australia^{[citation needed]}

While some may find regular briefs too restrictive, others may find boxer shorts too loose. A pouch or "over sized" pouch may be built in to add space and position the testicles forward and give the penis more room. Boxer briefs are commonly used in athletics instead of, or in addition to a jockstrap, but are common for everyday usage as well.

The boxer brief design provides form-fitting coverage for the midsection from the waist to the thighs and are worn on the waist. They are usually made of a combination of cotton and spandex or a soft, woven flannel material. Boxer brief designs can have either a keyhole fly, button (snap) front, pouch, or no fly at all. The waistband is usually a separate band of elastic material, often in a contrasting color to the cotton or flannel material that comprises the rest of the boxer briefs. The elastic band often has the name of the manufacturer (e.g. "Calvin Klein","DIM", "Croota" ) printed on it. There may also be additional elastic sewn around the bottom end of the thigh portion of the garment. Some boxer briefs have stitching on the rear to outline the buttocks and avoid a central seam.