Final answer:
A bulla is a large, fluid-filled sac found in the skin, often associated with certain skin conditions like impetigo.
Step-by-step explanation:
A bulla is defined as a large, fluid-filled sac that develops in the skin. It is an encapsulated sac filled with fluid, semi-solid matter, or gas, typically located just below the upper layers of skin. These are often associated with skin conditions like impetigo, where bullae are large, fluid- or pus-filled bumps on the skin, particularly around the nose and mouth, and can measure at least 5 mm in diameter. In such infections, bullae may fill and rupture, leading to larger, draining, encrusted lesions.