The Thai lunar calendar is a way of measuring time that is based on the cycles of the moon. Just like the Earth goes around the sun, the moon goes around the Earth, and each cycle takes about 29.5 days. So, a lunar calendar is made up of months that are based on these cycles.
In Thailand, the lunar calendar is still used for traditional holidays and special events, like the Songkran Festival, which is the Thai New Year. The calendar is made up of 12 lunar months, and each one starts with the new moon.
Because the lunar calendar is based on the cycles of the moon, it can be a little bit shorter than the solar calendar, which is based on the Earth going around the sun. That means that sometimes there are extra months added to make up the difference. These extra months are called "leap months."
Overall, the Thai lunar calendar is an important cultural and historical tradition in Thailand and is used to mark many important holidays and events throughout the year.