A Two-Seventy is a maneuver, not a formation. This means that it’s a pattern flown through the air, much like lazy eights or chandelles.
As the name suggests, a Two-Seventy refers to a turn of 270 degrees. Three-fourth around the protractor! Such a turn in itself isn’t very special. However, the formation incorporates altitude differences throughout the turn. From the perspective of the audience, it looks like the planes are performing a looping!
You can see the flown altitude differences in this schematic. At the beginning of the turn, the formation is flying relatively high. They then dive down, picking up speed. A bit later they pull up again, trading speed for altitude.
A fun fact about the Two-Seventy: only the leader knows about where he is throughout the turn. He also knows when to dive, when to turn, and when to pull up. The numbers 2, 3, 4 and so on certainly know what is about to happen but they rely on the leader for the commands to guide them. They are too focused on flying a tight formation to know how much of the turn has already been completed. The commands used for guidance by the leader are the following: “Two-Seventy, left-hand”, and “dive… start banking… and pull up”.