Every Thai has at least three names.
1. The sacred name they receive from the monk immediately after birth during the first blessing. Only the parents and the person himself know this name. Thais believe that knowledge of this name can give control over a person, call evil spirits to him, etc.
2. Official first and last name used in documents and identification cards. That's right - any Thai can change his name whenever he wants. One of my Thai friends has done this 3 times already “for good luck”. The process is very simple - visit the state office and submit an application. I don’t remember the exact cost, but it is affordable - something around 1000-3000 baht, takes 3-7 days.
3. Short names for everyday use. It is not a "nickname" because a nickname may be given by the community or friends and the name is chosen by them themselves, usually after consulting an astrologer or monk, and very often they visit the temple and ask the monks for blessings to use it. Parents also use this name to call their children, so it's definitely not a nickname. Parents of small children choose their first short name themselves.
Well, besides this, naturally many Thais have nicknames from friends or community.