At important celebrations such as weddings, festivals and holidays, birthdays and, especially, New Year festivities, Tibetans follow a tradition hundreds of years old of throwing roasted barley flour (called tsampa) into the air, calling out 'Tashi Delek' (pronounced much as it's written) which translates in quite a lot of different ways in English. Roughly, it indicates 'Blessings' or, of course, 'Good luck'.
This phrase is used, with or without the flour, by Tibetans living in Tibet, China, and all over the world, as a general greeting as well a celebratory cry.
Barley is the main crop of Tibet and tsampa is Tibet's main food; the term refers to the flour as well as to the dough, porridge, and so on, made from it.