再见 (zài jiàn): "zai-jian" (The "ai" sounds like the "ai" in "bait")
再会 (zài huì): "zai-hwai" (The "uai" sounds like the "way" in "away")
Both phrases mean "goodbye" in Mandarin Chinese.
* 再见 (zài jiàn) is the most common and general way to say goodbye.
* 再会 (zài huì) is slightly more formal and implies you will see the person again in the future.