Skin biopsy: Removal of a piece of skin for the purpose of diagnostic examination. Skin biopsy is most frequently done to diagnose skin growths, such as moles, or skin conditions, such as rashes. Different skin biopsy techniques are used in different situations. A shave biopsy takes a thin slice and can be used to remove superficial lesions. A punch biopsy takes a core and can be used to remove small lesions and to diagnose rashes and other conditions. Excisional biopsies are generally larger and deeper than shave and punch biopsies, and they are used to completely remove an abnormal area of skin (lesion), such as a skin cancer.