Question

what is the difference between T-minus and L-minus?

Answer 1

"T" means the time of the launch and the official start of the mission. "T minus 20 seconds" means 20 seconds before the launch. "T plus 20 seconds" means 20 seconds after the launch.

It refers to the days, hours, and minutes remaining in the scheduled countdown to launch, which occurs at L-0. The “L” stands for launch.