Glossary
Lineup
In one line: An ability throw prepared in advance, from an exact spot, so it lands in an exact place.
What it means
A lineup is an ability thrown from a memorized position and aim point so it lands exactly where you need it: a molly on the spike from far away, an arrow that reveals an angle, a smoke covering a choke from behind a wall.
Lineups are useful, especially for the post-plant, but they are not the heart of the game. The questions come first: why do I want that ability there, and when? A perfect lineup thrown at the wrong moment does nothing.
An example
After the plant you hide far from the site. You have learned a lineup that sends your molly onto the spike from there. When you hear the defuse start, you throw it without exposing yourself: the defender has to stop.