恭喜发财 (Gōngxǐ fācái) is THE Chinese New Year greeting - you'll hear it billions of times every Spring Festival. The full version is often followed by 红包拿来 (hóngbāo nálái, 'hand over the red envelope!'), a playful demand for money.
culture
In mahjong, 发 (fā) is the green 'fortune' tile, short for 发财. It's one of the three 'dragon' tiles and is considered lucky.
