Astrotraining is to use the agenda token on one scored AstroScript Pilot Program to Fast Advance another copy of it straight from HQ.
The strategy is infamous as by scoring all three Astroscript Pilot Programs in an Astrotrain an NBN Corp has easily scored 6 of the 7 Agenda points needed to win, all from scoring the first Astroscript agenda. Typically that first Astroscript is scored early in the game before the runner can break through some simple end the run ice, or by using other Fast Advance cards like SanSan City Grid or Biotic Labor. The seventh point required to win is frequently from a Breaking News, which as a 2-advance-cost agenda can be naturally Fast Advanced.