A growing stereotype amongst male teenagers. It is someone between a computer nerd and sports addict. While semi nerd's are usually highly intelligent, they arent very interested in sports, or corny video games and over the top maths.
A typical semi nerd may play a console video game such as medal of honor, or Halo, they have many friends of both genders, but usually play two to no sports.
It could be said that they aren't nerds but they do nerd related activities in a 'cool' way.
Sporty Person: Look at this semi nerd, playing his pokemon or what ever...
Semi Nerd: Halo bro, get it right.
Nerd: Im sooo smarter than you, what is (27x11)/cosine(2+1)
Semi Nerd: Umm, can you use it in a sentence?