Outside Critical Squares
As mentioned previously in K+p vs K endings the critical squares for a pawn on the 2nd, 3rd, or 4th rank are two ranks ahead, whereas, the critical squares for a pawn on the 5th rank are one rank ahead of the pawn.
In the diagram below the critical squares for White's pawn on d4 are: e6, d6,and c6 .
White's objective is to seize control of one of the critical squares. Typically, when the superior side has an option, it is better to head for the "Outside Critical Square", which tends to be more dificult for the opponent's King to reach. Here the outside critical square is c6.
So, with White to move there follows: 1.Kd5 Ke7 2.Kc6 and White occupies the critical square. The diagonal path taken by White's King, crossing in front of his pawn to get to the critical square, is a maneuver known as "the overpass".