Final answer:
The combination of the word parts 'derm' and 'logy' refers to dermatology, the medical specialty concerned with the study and treatment of skin diseases.
Step-by-step explanation:
The best definition for the combination of word parts 'derm' and 'logy' is dermatology, which is the branch of medicine that deals with the skin and its diseases. The prefix 'derm' is derived from the Greek word for skin, while 'logy' means the study of something. Dermatology involves the study and treatment of skin conditions, including those caused by dermatophytes—various fungi that feed on keratin in the skin, hair, and nails and can lead to cutaneous infections. The field also encompasses the understanding of structures such as the dermis, which is the second layer of human skin, situated between the epidermis and the hypodermis.