A person who has many of the internal qualities of a geek, however does not look or act like a geek.
A geek who has developed social skills.
If you want to know if the hot guy is a stealth geek, the ask him about Star Trek or Mac vs. PC.
Stealth Geek is a geek who processes more information, on average, in a better way, despite the fact the knowledge he processes isn't necessarily useful. The fact someone is a geek is "Stealthed" until someone within earshot of the "Stealth Geek" mentions video games, PCs, consoles, software, roleplaying games or some other such "uncool" item, at which point the "Stealth Geek" drops "Stealth Mode" and his geekiness spews out.
Most "Stealth Geeks" fit in with the popular crowd and bash geeks who don't seem "cool" right off the bat, at least initially.
I used to think Warian was cool, but he's a stealth geek.