The act of taking at LEAST a week (5 Days annual leave) off work/school/college/university to commence non-stop hardcore playing of Halo on the X-Box. Originating with Halo 2 on X-Box live, Halo Holiday is encouraged in some circles to improve Halo 3 play/rank/skill levels. Interaction with the outside world/humans is allowed only at the point of halo'ed out.
Colleague 1) Where the hell is Mike? He's not been in for a few days.
Colleague 2) He's back on Monday, he's been on a Halo Holiday.
Colleague 1) Geek.