What term is used for a collection of blood beneath the skin?

A hematoma is defined as a localized collection of blood outside of blood vessels, typically caused by the rupture of blood vessels due to injury. This collection can occur beneath the skin or within the body, leading to swelling and discoloration in the affected area. In this context, a hematoma specifically refers to a significant accumulation of blood that forms a mass, which can vary in size and severity depending on the extent of the injury.

While the term bruise is often used colloquially and can sometimes be associated with a superficial injury like a contusion, it generally refers to smaller collections of blood or damage to the skin and underlying tissue without the significant clotted blood mass that characterizes a hematoma. A contusion is also a type of bruise but typically involves more superficial tissue damage rather than significant blood accumulation. The term "swell" does not accurately describe a specific medical condition associated with blood collection.

In summary, a hematoma is a precise term used to describe the accumulation of blood beneath the skin or within body tissues, making it the appropriate choice for this question.