Which term would describe a very large bubble-like structure under the skin, often filled with fluid?

The term "bulla" refers to a large, fluid-filled sac or bubble that forms under the skin. Bullae are typically greater than 0.5 centimeters in diameter and can form as a result of various conditions such as burns, insect bites, or other skin irritations. They are distinguished from smaller structures, such as vesicles, which are also fluid-filled but are smaller in size.

In contrast, pustules are small, inflamed lesions filled with pus, indicating an infection or inflammatory process, while blisters, although similar to bullae, are generally smaller and can vary in cause. Understanding these distinctions is key in both clinical settings and studying dermatological conditions.