Phaser range

The phaser range was a facility aboard some starships that allowed Starfleet personnel to practice aiming and firing their phasers. It consisted of a circular stage set in a large empty area. The area around the stage was illuminated, but everywhere else was dark. Flashing spheres of light of different colors and moving at various speeds served as the targets. Two people could be accommodated in the range at any one time. 

When first arriving aboard Deep Space 9, Julian Bashir asked Odo if the station had an area where he could practice with his phaser. 

Guinan liked to practice on the USS Enterprise (NCC-1701-D)'s phaser range, and did so at a higher difficulty setting than Lieutenant Worf.