Draft is the stage before the game starts, during which teams take turns banning and picking characters. In Dota 2 these are heroes, and who bans and picks whom often shapes the entire game plan before a single key is even pressed in combat.
The draft works as a sequence of moves: first, the sides ban heroes they don't want their opponent to have, then they take turns picking their own. The order of moves and the number of bans depend on the tournament format and the game version, but the essence remains the same — it's a chess match where every pick responds not only to the current situation but also anticipates the opponent's next move.
Who makes decisions during the draft
Usually the decisions at this stage are made by the team captain — the same person referred to as the IGL (in-game leader), meaning the in-game strategist. He keeps in mind not only his own five players' strengths but also which hero combinations the opponent has used before, what's currently prioritized in the meta, and which picks cover the weak points of the lineup.
Why draft matters to viewers
To an outside observer, the draft might seem like a boring technical part before "the real game," but experienced analysts and casters break it down separately: a successful or unsuccessful hero lineup can decide the outcome of a match before the teams even step onto the map. A mistake in the draft — an open lane, weak resistance to a specific opponent strategy — is rarely compensated for by good mechanics alone during the match itself.
The word comes from the English "draft," which in a sporting context originally meant selecting players for a team, but in esports it became attached specifically to the stage of picking characters before combat.