What is the name of a holiday that marks the beginning of spring celebrated by Iranian and Turkic people?

Nowruz (means "new day") is the Iranian New Year, also known as the Persian New Year, which begins on the spring equinox and marks the beginning of spring in the Northern Hemisphere. It is celebrated worldwide by various ethno-linguistic groups, and falls on or around March 21 of the Gregorian calendar. Nowruz falls on March 20 in 2021.

The definition of Nowruz given by the Iranian scientist Tusi was the following: "the first day of the official New Year (Nowruz) was always the day on which the sun entered Aries before noon."

Nowruz survived the Muslim conquest of Persia of 650 CE. Later Turkic and Mongol invaders did not attempt to abolish Nowruz.

Nowruz was added to the UNESCO (United Nations Educational, Scientific and Cultural Organization) List of the Intangible Cultural Heritage of Humanity in 2010.

People start preparing for Nowruz with a major spring cleaning of their homes and by buying new clothes to wear for the New Year, as well as the purchase of flowers. During the Nowruz holidays, people are expected to make short visits to the homes of family, friends and neighbors.

The festival of Nowruz is celebrated by many groups of people in the Black Sea basin, the Balkans, the Caucasus, Western Asia, central and southern Asia, and by Iranian peoples worldwide.