When you say “Completez” to the croupier in roulette, you are “completing” the bet, or placing a chip on every corner it touches and every split that can be made from it.
So say you place a 17 and it comes up. You would then tell the croupier to “complete” the 17.
That´s a straight- up bet on 17, a corner roulette bet on the 14,15,17,18 then 13,14,16,17, then 16,17,19,20, and then 17,20,21,18.
Next a split bet on the 14,17, and 17,18, then 17,20, and then 16,17.
Do we recommend this bet? Not really. Unless you want to show off at the table, or impress a member of the opposite sex. It´s really only based on patterns on the roulette table which won´t improve your odds.