>>what does that mean?<<
A 45-slide "crash stop" is an emergency manuver used on mopeds to avoid or minimize collision risk/damage.
The moped is "muscled" to 45 degrees from it's original angle of travel, and leaned way over as the brakes are locked up and the rider drags the opposite heel behind him.
Done correctly, it puts a tremendous amount of rubber and braking power at your disposal and may prevent a collision.
If there is a collision however, it also puts the entire mass of the moped between you and whatever you hit, creating a "crumple zone" that may save your life.
Best practiced on the driveway before tried in real life.
Worth learning it, however.