Glossary
Callout
In one line: The shared name of a spot on the map, or a piece of information you give your team out loud.
What it means
The word has two uses. First: the names of places on a map (A main, mid, heaven, CT). Every map has its own, and the game shows many of them on the minimap. Knowing them lets you say where an enemy is in two words.
Second: the callout as information, what you tell your team. A good callout is short and says where, how many and what: "two A main, one low". Information first, everything else later. A long or messy sentence arrives too late.
An example
You die on B and have two seconds before you can no longer talk. Instead of "no way, how did he, he was right there", you say "one B back, Odin". Your teammates know where to look and what gun they are facing.