That means it is the volume of air flow corrected to standard temperature and air pressure. Therefore, SCFH translates to Nm3/hr (Normal cubic meters per hour).
If you have 300 cfm of air at 100 psi, you've got a lot more SCFM.
The purpose of using these units is specifically so that you can determine the number of moles of gas per hour. Specifying SCFM is equivalent to specifying the mass flow rate.