Wai is a form of Thai culture which represents various aspects of Thai honorific system. For example, wai shows Thai politeness, respect, honor, and friendship. Thais wai when greeting or leaving. Along with a wai, Thais usually say 'sawasdee,' which means 'hello' in English. The wai tradition has been succeeded to the present generation since Sukhotai Period, approximately A.D. 1238). Wai can also be used in articulating apology or gratitude. For these purposes, a person who wais usually says, 'khor-thod' or 'khob-khun,' respectively.
How to wai
1. Put the palms together. According to Buddhism, Thais call wai 'pra-nom-mue' (keep waiing all the time) or 'unchalee'. When waiing, put your palms together, straighten and press your finger tips together. Raise your palms to your chest and keep your elbows close to your body. When talking to priests and the royal family, Thais always 'pra-nom-mue.' When leaving these respectful people, the younger usually 'unchalee' them.
2. Bow your head. Wai can be in the form of 'wan-ta.' In so doing, Thais bow their heads and high their palms up until the index fingers touch their mouths or noses, depending on the person who they wai.