Hongbao

Hongbao () or red envelope is an envelope with money inside. In China, people give the envelope as a gift for special occasions. The red envelopes are most commonly given to children or single/unmarried adults during the Chinese New Year celebration, where Chinese families often gather together.
The red packet is also called “money warding off old age” (压岁钱; "yāsuì qián") during Chinese New Year.
Outside of China, similar customs have been adopted or are traditional across parts of Southeast Asia and many other countries with a sizable ethnic Chinese population. In the mid-2010's, a digital equivalent to the practice emerged within messaging apps with mobile wallet systems.
Origin of the hongbao.
According to Chinese legend, in ancient times there was a demon or evil fairy named "Sui" (祟). Legend says that Sui is totally black, except for its colorless, transparent hands. Sui—according to the said legend—appears every Chinese New Year’s eve and would touch a sleeping child’s head, causing mental illness.
This is why Chinese New Year celebration is practiced by staying up late during the new year’s eve, called "Shousui" or translated as “waiting for Sui”.
So, the elderly people started to thread coins with a red string, called "ya sui qian" or “money to suppress Sui”. The coins were given to children to entertain them, and to keep them awake to avoid "Sui"’s touch.
According to the same legend, eight noble fairies turned themselves into eight coins, protecting the children from "Sui." Thus, the story spread and everyone started to follow the same practice to protect the children. Over the years, the "ya sui qian" was replaced with the red envelopes—the "hongbao."