Final answer:
A bulla is defined as a large blister, which is a fluid-filled lesion measuring at least 5 mm in diameter. It can be seen in skin conditions like impetigo.
Step-by-step explanation:
A bulla is defined as a large blister. It is a fluid-filled lesion that measures at least 5 mm in diameter. Bullae can be seen in certain skin conditions, such as impetigo, where they fill and rupture, resulting in larger, draining, encrusted lesions.