The word "default" in esports slang means "by default": what a team does when it has no reason to do anything else. A default position is the place a player takes at the start of a round as their baseline. The term is most often heard in Counter-Strike 2 in relation to defense, although it is also used in other tactical games.
How the term sounds in the game
In ordinary voice-chat speech you can hear "you're on default," "go back to default," "his default is closer to mid." This means that on a given map every player has a habitual spot from which they start the round: behind a box, in a corner, at the exit of a zone. Such positions are chosen so that the player has cover, a view of the needed direction, and the ability to fall back if the pressure turns out to be too strong.
The main idea of a default is that it is universal. The defending team does not know where the opponent will go, so it evenly covers the key directions and gathers information: someone listens for footsteps, someone throws a grenade to scout, someone simply holds an angle. As soon as the first reliable information appears, the setup changes: players leave their default spots and help where the push has started. Such a move is called a rotation, that is, a quick transition to another part of the map.
Default and off-default
Non-standard positions are contrasted with the default position: an aggressive push out to meet the opponent, a "stack" (when several players gather on one spot, for example three of five defending one entrance), or an unusual angle meant to catch the opponent off guard. An off-default play works until the opponent figures it out; a default is reliable but predictable. That is why strong teams alternate both approaches and do not let the opponent get used to a single pattern of play.
"Default" refers not only to a place but to a whole set of actions. For example, a "default setup" on the defending side includes both the positioning and predetermined grenades that players throw in the first seconds. And on attack, a "default" often means a slow sweep of the map to gather information before the decisive strike.
Where the word comes from
"Default" came from the English word default, meaning "the standard option." In Russian-language gaming speech it became established both as a noun and as a modifier: "default setup," "default tactic." In a similar way, borrowings such as "setup" or "eco" entered the language of those who play and watch matches.
Analysis of default positions often appears in commentary as well: casters note that a team "moved away from the default" if a round went according to a non-standard scenario, and assess whether that improvisation was justified. It is precisely the ability to leave the usual scheme at the right moment that usually distinguishes a well-coordinated team from one that has simply memorized setups.