Three stars in a row
The san-rensei is three star points in a row along one side. It trades corner security for speed: a whole side becomes a framework for just two moves, and anything intruding into it can be attacked from every direction. Star points are light — each 4-4 stone keeps both the corner and the side in play — so the san-rensei player builds influence fast, then attacks the invader with the framework at their back. Side extensions and enclosures are big points too, but completing the row is the move that makes the whole side work as one.