Yes that is Mcrit as I defined in my previous post.
... it is the speed at which somewhere on the airframe the local flow will go sonic.
To explain further if required (apologies if it's not), The acceleration you describe is one of the basic theories of how a wing produces lift. It is shaped in such a way that the air going over the upper side is accelerated. According to Bernoulli's principle, whenever a fluid (air in our case) is accelerated, there is a drop in pressure. When you have a lower pressure on top of the wing compared to a higher pressure below the wing, the wing will want to move into the area of lower pressure thus 'lifting'.
The problem of Mcrit is that the airspeed (or Mach no.) of the airframe is not equal to the speed of the air everywhere on/around it. It doesn't take into account this acceleration over the top of the wing. This means that at some Mach no., you are going to have the speed over the wing reaching the speed of sound / going sonic / Mach 1.0.
When this happens the properties of the air change, and you get energy losses and extra drag, which is NOT a desired thing, thus you avoid letting the air over the upper surface reach a sonic speed, and the only way that you can do this from the cockpit is to not exceed Mcrit, which is the speed that the clever people have worked out above which a sonic flow will happen somewhere (for example, M0.85).