A dart in a double bullseye
The bullseye is the yellow circle at the centre of this archery target
The bullseye, or bull's-eye, is the centre of a target, and by extension the name given to any shot that hits the bullseye. By extension, the word bullseye can refer to any design or pattern featuring prominent concentric circles, visually suggesting an archery target, and "hitting the bullseye" is a term for an unexpectedly good success.
Hitting the bullseye is worth 10 points in target archery and 25 points in darts. In darts, a "double bullseye" is a smaller, inner circle and counts for 50 points.
Popular culture usage 
See also