The 3rd and final attacking shape is the square. Since it represents a pass into open space rather than
to a teammate’s feet, it’s probably the most difficult shape to visualize and execute. However, once you get it, your ability to move the ball around the field will be virtually unstoppable.
Please click on the soccer field below right to enlarge. Yellow cones represent the square.
Example #1 – Backward Square Pass 
A1 has the ball and is being challenged. A1’s teammates are in great attacking shape. A2 and A3 have formed a triangle giving A1 wide passing options either left or right while A4 has completed the diamond shape (with her other 3 teammates) giving A1 a passing option high down the field. However, the red defense (red arrows) are positioned to prevent all of these passing options. A1’s best option is a square pass. A2 yells “square”; A1 makes a lateral pass into open space (dotted arrow is ball movement); A2 retreats (blue arrow is player movement) to receive this pass directly across (square) from A1. Obviously, this same square pass could have been made by A1 to A3 on the other side of the field. Ball possession rather than ball advancement is the objective of this classic square pass.
Example #2 – Forward Square Pass
A2 has the ball and is being challenged. Once again, the blue team is in great attacking shape (the triangle/diamond). A2 has two passing options. She could easily make a back pass to A1 who is unmarked. However, A2 can make a thru pass down the field (dotted arrow is ball movement) to A4 who cuts across the field (blue arrow is player movement) to receive this square/thru ball into open space. Communication between teammates is a key when passing to open space. A2 yells something like “down the line” to tell A4 to run across the field to receive a this thru ball. As opposed to the backward square pass, the objective of the forward square pass is ball advancement rather than ball possession.
Video Clip
We practice the square pass often in our 3v1 "Monkey In The Middle Keep Away" game. Here is a NSCAA instructional clip of this activity. Notice the movement "along the square" to support your teammate (with the ball) a passing option both left and right.
NSCAA Instruction – Movement Along The Square
Summary
The square is the third attacking shape representing passing options to space rather than to feet. Once you see the square, you’ll know which way to run to receive an open pass from a teammate. Generally, A1 and A4 (top and bottom of the diamond) move laterally to complete a square pass while A2 and A3 (sides of the diamond) move vertically to complete a square pass.
The triangle, diamond, and square are used by all players (including the goalie) when you gain possession of the ball. This includes all set pieces (throw in, kick off, goal kick, corner kick, and other free kicks except the penalty kick). It’s micro-tactics; that is, the small game inside the big game.