What medical term describes applying a drug on the surface of the skin?

The term that best describes applying a drug on the surface of the skin is "topical." This refers specifically to medications that are intended for local effects and are directly applied to the skin or mucous membranes, allowing for localized treatment without widespread distribution throughout the body. Topical preparations are commonly used for dermatological conditions, delivering the therapeutic agent directly to the site of action.

In contrast, "transdermal" refers to a method of drug delivery through the skin into the systemic circulation, typically using patches or gels designed for absorption into the bloodstream. "Intradermal" involves injecting a substance into the dermis layer of the skin, which is a different method of administration. "Subcutaneous" relates to injecting substances into the layer of fat beneath the skin, intended for systemic effects rather than localized treatment like topical medications.

Thus, topical accurately captures the essence of applying a drug directly onto the skin for localized therapeutic effects.