Flag Off or 'Flagged Off means official start or beginning of an event or undertaking.
In this a piece of cloth, usually rectangular in size, and of distinctive color and design, is used as a symbol, standard, signal, or emblem and waved.
[1][2] It is an idiomatic expression, indicating the commencement of some event- usually involving travel or movement.
On the other hand, for stationary events, such as a sporting tournament, political summit, literary meet, etc.
[5][6] A similar significant flag off event happened when the then Railway Minister Mamata Banerjee flagged off India's first ever point-to-point non-stop train, the Sealdah-New Delhi Duronto Express, from the Sealdah station in Kolkata on January 20, 2013.