Organomagnesium halides, $\ce{RMgX, having a carbon–magnesium bond (or their equilibrium mixtures in solution with $\ce{R2Mg}$ + $\ce{MgX}$).
Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1338 [Terms] [Paper]