IFLOLS, I know I didn’t capitalize the last letter, but it’s 4:30 in the morning here.
Improved Fresnel Lens Optical Landing System. Colloquially: the Meatball. When you land on the carrier it’s the big array of lights that hang off the left side of the ship. There is a fixed set of green lights that represent the optimal glide slope for the optimal landing. A centrally mounted amber light (the ball), traverses up and down a track. It’s position relatively to the green lights indicates the pilot’s current position above or below glide slope. A low ball is corrected with power, a high ball is corrected by easing off the power. If you’re too low, the ball will become red. if you are too high or too low, you’ll get a wave off signal.