Depending on which layer of the skin, it could be subdermal or subcutaneous (Sub: Under, Cutaneous: The skin). The prefix hypo- means below and the dermis is the bottommost layer of skin. So the medical term for beneath the skin is hypodermic.
The medical term for any swelling is called a lump
Subcutaneous
Dermoid is the medical term meaning skin-like
Bruise (medical term = ecchymosis)
Pyoderma is the medical term meaning any purulent skin condition.
The medical term for a fatty deposit under the skin is lipoma.cellulite
Hyperpigmentation is the medical term meaning excessively darkened skin.
Acrochordon is the medical term meaning skin tag. Skin tags can occur in areas of high friction.
Dermatomycosis is the medical term meaning fungal disease of the skin.
Sub- is the prefix of the term subdermal, meaning below the skin.
The medical term meaning Tb skin test is Mantoux. It's a term that refers to a skin test to check for tuburculosis.
Hyperpigmentation is the medical term meaning excessively darkened skin.