Final answer:
A nodule is a deep, solid, raised bump on the skin, which is elevated, firm, and can grow in size. It differs from flat discolorations or blisters as it is more solid and often located deeper in the skin.
Step-by-step explanation:
A nodule is best described as a deep, solid, raised bump on the skin, which makes option C the correct answer. Unlike smooth spots of discoloration, which are flat and primarily affect skin pigment, nodules are elevated, firm, and often growing. Unlike blisters or fluid-filled sacs, nodules are typically much more solid. They can be compared to encapsulated sacs that can contain fluid, semi-solid matter, or gas, but are generally more solid in nature and are located more deeply in the skin. Certain types of nodules like nodular melanoma can be characterized by the mnemonic ABCD: Asymmetry, Borders that are irregular in shape, varied Color shades, and a Diameter larger than 6 mm, along with being Elevated, Firm, and Growing.
This detailed characterization aids in distinguishing nodules from other skin abnormalities and underscores their clinical significance.