PokéCommunity's Battle Stadium has a ranking system called "PC Ladder", which is a system that we use to determine who the best battlers are. When 2 people engage in a "Ladder Match", it means that the battle will count towards the players' rankings in the Ladder Match. Whoever loses gets -1 point in the Ladder Stadistics, and whoever wins gets +2 points to their Ladder Stadistics.
That's what you need to know about it.