Final answer:
Squamous cell carcinoma is the second most common type of skin cancer and is characterized by firm, red nodules or flat lesions with scaling or ulceration.
Step-by-step explanation:
Squamous cell carcinoma is the second most common type of skin cancer. It occurs in the squamous cells of the epidermis, which are flattened, keratin-filled cells in the upper layers of the skin. Squamous cell carcinomas may appear as firm, red nodules or flat lesions with a scaly or crusty surface.