ตักบาตร or "TAK BAT" means giving alms to monks.
Every morning at dawn, monks are going out to get some food. Thai people fill monk bowl with rice, soft drinks, cakes and so on... This ceremony is called "TAKBAT". Thai people are making good deeds ("THAM BUN" - ทำบุญ). To make the action as good as possible, people must give the best food they have. They should not be avaricious by giving cheap food. Monks deserve the best. By offering food to monks, they are supposed to give food to relatives who died already.