These were my criteria when choosing a domain name:

1. It's available.
2. I can say it out loud and expect people to know how to spell it.
3. It doesn't look weird or silly.

/impulse is a console command for the Quake series of games (prior to Quake 3) and games based on these Quake engines (e.g. Half-Life). In Half-Life, the command /impulse 101 gives the player all weapons, ammunition, and items. After trying several domain names that were taken, I thought of /impulse 101 for some strange reason (I hadn't played Half-Life in a long time, and I hadn't used any console commands in an even longer time), and I was astonished to see that impulse101.org was not taken! Since it fit my primary criteria, I took it.