Thai "WAI"
The Thai greeting ไหว้, wâi
The word often spoken with the wai as a greeting or farewell is sàwàtdi As well as being a greeting, a wai is a method of showing respect in different degrees.
"WAI" for Praying to the Buddha ,Greeting,Thank you, saying good bye ,sorry and apologize. We don't 'Wai' to everyone. Thai people pay respect to someone who is older or as senior that we respect them.
As a foreigner "wai" to important people,senior in working places and Thai family as soon as possible. If someone "wai" you first, then received their "wai" just "wai" them back.