Originally coined in 1995 in the small town of Mooresville, NC. A computer jock was someone who exhibited the traits of an old school nerd, but was also active in athletics. In a typical day they could be found acing a test and then being called to the principle's office for sleeping through another class. After school you'd likely find them at practice, whether that was track, cross country, basketball, or football. After practice however they could be found replacing their 9600baud modem with a brand new 14.4k so they could dial into the new BBS in town.
Now-a-days, that same person is likely working in IT, software, or is some kind of engineer. They likely still have computer parts laying around in their closets and can speak fluent nerdian if they run into another nerd. But outside of work you might be surprised when you discover their nerd side. You'd likely find them hiking up a mountain, rock climbing, surfing, running, mountain biking, kayaking, or some other outdoor sport. They can fit in socially and will likely be around other active people. You'll occasionally see them slip up and let the nerd side venture into that portion of their life when they discover someone else in the group is a computer jock as well... the conversation could quickly go from sports to the latest open-source java framework or what makes ruby, or java, or python better than other languages.
You'd never guess it, but that guy is a computer programmer. He used to be a complete nerd, but then he got lasik done and got into triathlons, now he's a computer jock.