Traditionally, a suicide pool is you pick one team per week to win straight up. No point spread, just to outright win. If you win, you advance to the next week. If you lose you're eliminated.
The catch is that you can only pick a team once. So for example you take the obvious pick in Week 1 and go Baltimore Ravens over New York Jets. Then you can no longer pick the Ravens the rest of the year.
Kidding about the Ravens being the obvious pick in Week 1, and to be honest there really is no great pick Week 1 this year. Currently I'm leaning towards Titans over Raiders for my big money pool, I just don't trust Vince Young completely. Not many other great options though.