Well, "chronic" means ongoing, something that happens frequently over a long period of time. If you had chronic headaches, that would mean you'd have a lot of them and it would be a problem you would have had for a while. You know what masturbation means, right?
So "chronic masturbation" would mean someone who masturbated a lot, and had done so for a long time.
Is this necessarily a problem? No. I think that using the term "chronic masturbation" is more a value judgement than it seems on the surface -- because it implies that there is a right and wrong amount of masturbation, and that more than that "right amount" is bad in a sort of medical way.
And that's just not true. The only person who can make a decision about whether or not they are masturbating too much is that person him or herself. If it feels uncomfortable, if someone is feeling obsessed about masturbating, or if masturbating is getting in the way of their ability to do other things they need to do in their life, then perhaps they need to think about whether they're doing it too much and need to ease off.
But really, if masturbation isn't a problem, then it just isn't a problem.
Start a Revolution -- Stop Hating Your Body!