Ylide
The ylide is an electrically neutral molecule that has a negative carbon with an unshared electron pair (usually a carbanion) adjacent to a positive heteroatom (typically nitrogen, phosphorus, or sulfur), where both the atoms have full octets (eight electrons in their valence shell).
The bond between the carbanion and positive heteroatom is best described as a polar covalent bond with significant ionic and double-bond character, depending on the ylide type.