English (Source)
Your Commander's experience. Gained at the end of each wave and through other various means such as destroying certain buildings, artifacts, etc. When leveling up you get to choose from a pool of rewards at the end of the wave.
English Translation
Your Commander's experience. Earned at the end of each wave and through other means like destroying specific buildings and artifacts. Upon leveling up, choose from a selection of rewards at the end of the wave.