Here is another explanation:
There is an increase in the speed of airflow over certain parts of an A/C (i.e. over the top surface of an airfoil). However, the A/C may be travelling at a speed well below the speed of sound, but the airflow relative to certain parts of the A/C may exceed the speed of sound. Therefore, that Free Stream Mach Number at which any Local Mach Number reaches 1, is called the Critical Mach Number.
So, no, jets will be cruising well below Mcrit. But through design changes the Mcrit can be raised to delay shock-induced separation.
At a point about 5-10% beyond Mcrit, a sharp rise in drag is perceptible. You need powerful engines to go beyond Mcrit.
On pax jets TODAY, you will not experience Mcrit or higher under "normal" conditions. Maybe Dassault will build the next supersonic pax jet.