A trade (from English "trade" — exchange) is a situation where one player dies to an enemy shot, and a teammate standing nearby almost immediately fires back and kills that same opponent. In effect, the team "trades" one of its own deaths for the enemy's death, so the numerical advantage on the map isn't lost for nothing.
The word comes from English CS terminology and has settled into Russian gaming slang without translation, as "трейд". People say "затрейдить" ("to trade"), "взять трейд" ("to get the trade"), "его затрейдили" ("he got traded") — meaning a player died, but a teammate immediately avenged him with a kill. Sometimes the variant "трейд килл" (trade kill) or "трейд фраг" (trade frag) is used — referring to a specific kill counted as a trade.
A trade isn't accidental — it's the result of positioning. Experienced players deliberately keep a distance that lets them hear the shot or see their teammate die and react instantly: adjust their aim and pull the trigger before the enemy can retreat to cover. Standing too close is dangerous — you can die from the same grenade or burst as your teammate, while standing too far away makes trading impossible altogether.
In team tactics, trades are planned in advance. For example, during a site execute, one player goes first and "presses" an angle, baiting the enemy into shooting, while a second player positions slightly behind specifically to pick up the trade. The IGL (in-game leader, the player who builds out the tactics) often explicitly assigns roles for trade positions when executing onto a bombsite.
Trades are especially important in clutches (situations where one player is left facing several opponents) — if the attacking side loses players without getting kills in return, the remaining defender gains the advantage. Conversely, a team that consistently trades deaths evens out the number of players alive faster and pushes through the round.
At the professional level, trade kill statistics are one of the metrics used to evaluate team play and in-squad support: a high trade percentage points to coordinated teamwork rather than just individual skill.