@feha it's an advanced stat for offensive performance (baseball is great for stats with how segmented it is):
http://m.mlb.com/glossary/advanced-stats/weighted-runs-created-plus
@feha it's weighted Runs Created plus. It's a combined measure of how well a player performs in a variety of offensive measures expressed on a standardized scale where 100 is the league average performance and each point above or below represents one percentage point deviation from that mark.
120 would be a player who is 20% better than the average mark. By MLB standards that would make a player pretty good. around 140 or so is about where star players start popping up. I don't know the scale might be different in Japanese baseball given how differently players of that league perform (more hits, less walks, less home runs)