What does M/Z mean?

M/Z represents the mass to charge ratio. M stands for the mass of an ion and Z stands for the formal charge of an ion. The horizontal axis in a mass spectrum is indicated in units of m/z. Most ions have a charge of +1, thus the m/z ratio is equal to the mass itself. Since the m/z ratio gives the molecular mass of the compound, it can be used with the fragmentation data to identify the structure of the compound.