When you go from doing other stuff to doing nerd things for about a week to a month; such as jailbreaking your iPod Touch, or Youtubing videos on help on how to do something with your device. After you lose interest, you go back to the same old normal stuff you do.
Mark: Dude, you should come chill with us.
Tim: Nah, I think I'm gonna jailbreak my iPod Touch this week.
Jeff: He's on his nerd phase.