X-axis is number of points, Y-axis is the probability of finishing on that many points, based on Caley's statistical models. And the number atop each bar is the probability of winning the title if we finish on that many points.
For example, Spurs have roughly an 18% chance of finishing on 78pts and, if we did, we'd have a 41% chance of being crowned champions.
If you go over to Michael Caley's Twitter feed, you'll find some explanation. The model predicts game outcomes based on the number and quality of chances each team creates and concedes, running every match left in the season and adding it all up. Obviously, it's only a model, but it's interesting stuff.
Caley also features on
www.cartilagefreecaptain.com, which is worth a read.