Inspired by this entry of Roy's, I dug up a simple and ever so slightly bilingual statistics primer which explains:

The notorious hensachi (偏差値, deviation value) used for judging your ability in schools (in Japan) is nothing but a transformed value from this standardized normal distribution; change 0 into 50 points, and change the unit 1 into 10 points, and the resulting value is the hensachi.

So, unless I am about to embarrass myself (and I am sure my better-informed commenters will correct me if so), a hensachi of 40 would mean that 84.15% of the other students in your sample achieved better results than you.

Yeah, that is pretty bad.