Greetings
Thai greetings often involve a wai. To wai, the hands are raised as if in prayer and the head is bowed.
There are strict rules concerning who and how to wai. Generally, the younger person initiates the wai. The lower the head is bowed, the more respect is shown. As foreigners are usually not expected to know the wai etiquette, mistakes will be excused. However, if you are not sure how to wai, it is generally better not to wai at all.