A guy who's helluva good when it comes to fixing 'puters. Very common at universities, research labs etc. You'll be his best friend if you talk to him about Linux, Mozilla, HTML/PHP etc. As far as appearance is concerned, computer geeks can be placed in two groups: 1) the uglier one including fat, sluggish, bald C.G.'s or 2) thin and often tall ones, usually with hair of middle length, aware of their health and hygiene- so they never stink. Usually seen in glasses that go well with their beautiful faces. There are also female computer geeks, but they're rare and I didn't see many of them- most of them looks beautiful. Whoa, there are no ugly women, but sometimes you run out of wine.
Read "Linux for advanced users" everyday, spend 5 hours a day googling, write some programs and be exceptionally charming- they'll recognize a computer geek in you.