A hollow point bullet is a bullet that is designed to expand upon entering a target. Unlike a full metal jacket bullet, the jacket metal does not cover the entire bullet and an area near the nose is left uncovered. There is a pit present in the front of the nose (compare to soft point bullet, which has exposed lead but no hollow). When the bullet strikes a soft target, the pressure in the pit forces the ring of lead around it to expand greatly into a mushroom-shape. This causes considerably more soft-tissue damage than had the nose stayed intact. Generally, ideal performance of a hollow point bullet occurs when the bullet expands in a uniform shape, to the full depth of the hollow (or slightly more), and does not fragment or, in the case of jacketed bullets, shed its jacket. By expanding to a uniform diameter and retaining full weight, the bullet can be designed to penetrate to a consistent depth, causing maximum energy transfer to the target with minimum risk of overpenetration.

The Hague Convention prohibits the use of expanding or fragmenting bullets in warfare (often incorrectly believed to be prohibited in the Geneva Conventions), but hollow point bullets are one of the most common types of civilian and police ammunition. In fact, in many jurisdictions it is illegal to hunt game with ammunition that doesn't expand, and many target ranges also forbid full metal jacket ammunition (which is more likely to ricochet).

In slang, the hollow point bullet is also referred to as the dum dum, and is similar to the cross point which uses two slits instead of a pit. Recreational shooters often refer to hollow points as "JHPs", from the common manufacturer's abbreviation for "Jacketed, Hollow Point".