DNS Leaking and bad name serves

Hi all.. My boss just got off the phone with a company that was doing SEO for us. Basically he called me just to rant about their crappy service.

He wanted to know why our sites weren't getting more traffic with their services and they threw a couple terms at him that I'm unfamiliar with.

Apparently we have a bad name server, and our dns is leaking? I've tried googling this but I haven't really had much luck in figuring out exactly what that means, and how it would effect our site's ranks.

Any tips, or even pointers towards the right topics to search for? thanks!