Critical Mach Number
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At the risk of duplicating what has already been said;
As subsonic air flows over an airfoil (or wing), it accelerates, reaches a maximum speed and then decelerates toward the trailing edge. Thus, the Mach number of the flow increases and then decreases. The magnitude of this change depends on the airfoil shape and the angle of attack. Therefore as you increase the freestream Mach number, the highest local M on the wing surface may exceed 1 long before the freestream Mach number reaches 1. The value of M at which the highest M on the airfoil first reaches 1 is called the critical Mach number, or Mcr. Obviously Mcr is less than 1 for anything with any thickness at all.
Twenty years ago all transport aircraft in production were often defined by whether they had "supercritical wings" or not. The term had common currency in magazines like "Flight". The A300 did not, the A310 did (or was it only a semi-supercritical wing on the 310- anyone?). The Boeings from 75/767 onwards had supercit wings, characterised by having a "roof section" - an airfoil profile with a broad, flat upper surface without a clearly defined point of maximum camber, so no dramatic rise in local Mach number and no dramatic B47-style shock stall.
As to what the numbers are for different aircraft, I don't know. But logically there should be a small but significant jump in Mcr between the old generation and the new, by virtue of the supercritical sections now used.