Glossary
Double peek
In one line: Two players swinging the same angle together, so the enemy cannot kill both.
What it means
In a double peek two teammates peek at the same moment, side by side or from two close spots. The defender watching that angle has two targets: even if they kill the first, the second has time to kill them.
It works against a single defender or a sniper. Against two ready opponents it can turn into a coin-flip 2v2. It needs timing: if one player comes out half a second later, it is just a repeated peek. Count it out loud ("three, two, one, go").
An example
An enemy Operator is holding a long line into a site. You and a teammate stand on both sides of the opening and swing together. The Operator takes one of you, but the other kills them before they can chamber the next shot.