A site is one of the two bomb plant zones on a CS2 map (the other is B site). It is where terrorists can plant the bomb, and where counter-terrorists can either prevent that or defuse the bomb after it has been planted. The zone is marked on the floor with a large letter, and in the game, the player carrying the bomb gets the option to start planting as soon as they enter it.
How the word sounds in the game
In voice chat, A site is almost never called by its full name. More often you hear a short "ay," "ayka," or simply "on A." Phrases like "going A," "everyone A," or "A is open" mean that the team is choosing the direction of the attack or reporting that the path to the site is clear. The phrase "A default" describes the standard setup on this site: players take their usual positions without taking risks too early.
The term "A retake" is a separate one: it is an attempt by counter-terrorists to regain control of the site after the bomb has already been planted. A retake (from English "retake," meaning "to take back") relies on a coordinated entry from several sides and on grenades that keep the terrorists from calmly defending the bomb.
Why A site matters in tactics
Every map has its own geography: the approaches, cover, and distances to the sites differ, so the same A site is defended and attacked differently on different maps. The general logic, however, is similar. Attackers choose where to push, A or B, and often imitate one option in order to deceive the opponent and strike at the other. This move is called a fake: through deliberate activity, the team makes the defenders shift their forces to the wrong place.
Defenders, in turn, distribute players between the two sites and cover for one another: if pressure appears on A, part of the team must move over to help in time. A mistake in such a rotation is a typical cause of lost rounds even for strong rosters.
An example from practice
A typical situation: the terrorists gather on one flank, throw smokes and flashes, and go onto A site, while the defenders understand from the sound and from teammates' information that the main strike is going exactly there. One of the counter-terrorists calls for help by voice: "A is heavy, need a rotation." The team decides who to send over, and if they do it in time, they manage to meet the attackers on the approach; if it is too late, they switch to a retake.
Where the term comes from
Labeling the sites with letters came from the early versions of the Counter-Strike series and has survived to this day: a bomb can be planted at the "A bombsite" or the "B bombsite" (bombsite meaning "the place where the bomb is planted"). The Russian-speaking community shortened this to "точка А," "эйка," and simply "А," preserving the brevity that is needed in quick communication between players during a round.
For a viewer, understanding these words is useful during broadcasts: when a commentator says that a team is "pushing hard on A" and then "outplaying on B," it means a change in the direction of the attack. The scheme goes back to the basic logic of the mode: two sites force defenders to split their forces and attackers to look for a weak spot.