The predominant religion in Thailand is Buddhism, specifically Theravada Buddhism. The religion practiced in Thailand is somewhat unique to other Buddhist nations, having been infused with many outside elements. Hindu practices and traditional Chinese beliefs have influenced local beliefs to an extent, with animist beliefs playing a large role in making Thai Buddhism what it is today.
You will see, for example, many Thai people wearing amulets or carrying talismans, despite Buddhism prohibiting attachment to material objects. Belief in ghosts and spirits is strong in Thailand, stemming from traditional pre-Buddhism beliefs, and you’ll notice spirit shrines in all manner of places.