When first falling-in for a flight or platoon formation, after the dressing to the right, the leader of the formation (Drill or Training Instructor or even the Drill Team Commander) might use a term that some seem to be unfamiliar with, “If you are taller than the person in front of you, tap him on the shoulder and move up!”
The formation is given Right Face (facing the element/squad leaders), told “If you are taller than the person in front of you, tap him on the shoulder and move up!” and then given Right Face again (facing to the rear of the original formation)), told “If you are taller than the person in front of you, tap him on the shoulder and move up!” and sometimes given Left Face (facing the element/squad leaders again) and told the same thing for the last time or given About Face to resume the original formation.
To abbreviate this relatively long sentence, the term, “Taller-Tap!” is used. It’s not “tall or tap” or “tall tap,” or any other combination of words, just “Taller-Tap!”
Do not give, “If you are shorter than the person…” This sequence is to ensure the flight/platoon is formed up with the tallest people at the front and at the marching right. Note! If you want shorter people in front, then give “Left Face” in place of each “Right Face” above.
Update: From AFMAN 36-2203, Drill and Ceremonies
4.3.2. To size the flight, the flight commander faces the flight to the right (from line to column formation) and has taller personnel (except the guide, element leaders, and flight sergeant) move to the front of the flight according to height. The flight commander then faces the flight to the right (from column to inverted line formation) and again has taller personnel (except the flight sergeant) move to the front of the flight according to height. The flight commander faces the flight back to the left (column formation) and continues this procedure until all members are properly sized.
And now you know. :-)