Experience

Experience (short form xp) is the numeric stat you need in order to level your character. It can be obtained by completing various tasks like killing mobs.

cap

Caps are the maximum xp you will usually get for defeating a mob. Each total level has its own limit.

Overcap

It is possible to get more xp than your cap by defeating a particularly tricky mob for your level. This is rarely happens more than a few times for the same mob.