Songkran is the Thai New Year's national holiday. Songkran is on the 13 April every year, but the holiday period extends from 14 to 15 April. In 2018 the Thai cabinet extended the festival nationwide to five days, 12–16 April, to enable citizens to travel home for the holiday. In 2019, the holiday was observed 12–16 April as 13 April fell on a Saturday. 

The word "Songkran" comes from the Sanskrit word saṃkrānti, literally "astrological passage", meaning transformation or change. It coincides with the rising of Aries on the astrological chart and with the New Year of many calendars of South and Southeast Asia, in keeping with the Buddhist calendar.

The New Year takes place at virtually the same time as the new year celebrations of many countries in South Asia like China (Dai People of Yunnan Province), Laos, Myanmar, Cambodia, Nepal, Bangladesh, India, and Sri Lanka.

In Thailand, New Year is now officially celebrated on 1 January. Songkran was the official New Year until 1888, when it was switched to a fixed date of 1 April. Then in 1940, this date was shifted to 1 January. The traditional Thai New Year Songkran was transformed into a national holiday.

The Songkran celebration is rich with symbolic traditions. Mornings begin with merit-making. Visiting local temples and offering food to the Buddhist monks is commonly practiced. On this specific occasion, performing water pouring on Buddha statues and the young and elderly is a traditional ritual on this holiday. It represents purification and the washing away of one's sins and bad luck. As a festival of unity, people who have moved away usually return home to their loved ones and elders. Paying reverence to ancestors is an important part of Songkran tradition.

The holiday is known for its water festival. Major streets are closed to traffic, and are used as arenas for water fights. Celebrants, young and old, participate in this tradition by splashing water on each other. Traditional parades are held and in some venues "Miss Songkran" is crowned. where contestants are clothed in traditional Thai dress.

According to en.wikipedia