Final answer:
A flat elevated surface found on the skin or a mucous membrane is described as a C. plaque, which is different from other skin lesions such as nodules, pustules, and macules.
Step-by-step explanation:
A flat elevated surface found on the skin or on a mucous membrane is called a plaque. This term is used in dermatology to describe a specific type of lesion that is characterized by its flat, elevated appearance above the surface of the skin. Other options like nodules, pustules, and macules also refer to types of skin lesions, but they have distinct characteristics that differentiate them from plaques. Nodules are typically firmer and extend deeper into the skin layers, pustules are small, inflamed, pus-filled lesions, and macules are flat spots that are not raised above the skin's surface.
Therefore, the correct answer to the question is 'C) Plaque'. Plaques can be the result of various skin conditions and are often seen in diseases like psoriasis. By comparing with the characteristics given - flat and elevated - it is apparent that plaque is the correct terminology for such lesions.