What is the term for the build-up of fluid under the skin?

The term for the build-up of fluid under the skin is referred to as edema. Edema occurs when excess fluid accumulates in the body's tissues, leading to swelling. This condition can affect any part of the body, but it is commonly observed in areas such as the legs, feet, and around the eyes. The fluid buildup is typically caused by various factors, including inflammation, injury, or issues with the circulatory system.

In contrast, hydration pertains to the amount of water in the body and does not directly relate to fluid accumulation under the skin. Inflammation refers to the body's response to injury or infection, which can lead to edema as a secondary effect, but it does not describe the condition itself. Necrosis involves the death of cells or tissues and is not associated with fluid buildup but rather with damage and dysfunction in body structures. Each of these terms has distinct meanings and implications in veterinary medicine, but edema specifically addresses the fluid accumulation issue described in the question.