Canon EF-M mount explained
Compact system cameras don’t have a mirror like an SLR, which means the lens mount can be moved closer towards the sensor to make the camera smaller.
As a result, Canon’s existing EF and EF-S lenses can’t focus light on the M’s sensor and they aren’t compatible with the new camera without an adaptor to move them further away from the sensor.
There are currently just two lenses with the EF-M mount, the EF-M 18-55mm f/3.5-5.6 IS STM and the EF-M 22mm f/2 STM. There is a 1.6x focal length magnification factor when they are mounted on the M.
The STM in the lens name stands for Stepper Motor, and this is used to produce a slower, smoother focusing transition during video recording. These lenses are not compatible with Canon’s SLRs.