Demi is a prefix meaning "half", loaned from French; for example, demi frere which means "half brother" or demi soeur which means "half sister". Demi-glace is made by simmering and reducing by half a mixture of half brown stock and half espagnole sauce.

Demi also has Latin roots as a feminine given name, originally a nickname form of Demetria, the feminine form of the masculine name Demetrius, which is itself the Latin and English spelling of Greek name Demetrios.

Demi is uncommon as a surname. People with the given name Demi include: