The 0  (single zero) and the 00  (double zero) are the green slots on the roulette wheel. These pockets could receive a 35:1 payout if hit straight up. If there's a split, the payout could be 17:1. This type of bet is somewhat risky, but the payouts could be worth it.
What are the odds of hitting green in roulette? The odds for green in roulette depend on the version of the game. Since the American wheel has two green pockets, the odds of hitting either of them are 2-in-38, or 5.26%. In the European format, this drops to just 2.70% since there is one only green pocket on the wheel.