Ritual and respect
Wai
ไหว้
What it means
The Thai greeting: palms together, a slight bow of the head. At a gym you wai your trainer at the end of a session, and it is the single easiest piece of respect to get right.
Height matters. Hands higher and head lower for someone senior, and you do not need to match a monk or an elder exactly to be understood as polite.
You are not expected to be perfect at it. You are expected to do it, and visitors who never do are noticed.
Related
Words that go with it
Kru
Teacher. Used as a title before a trainer name, and the word at the centre of the sport, since the wai kru itself is a bow to the teacher.