Chunyun - the travel season in China, which usually begins 15 days before the Chinese New Year and lasts for around 40 days. In 2016 it was predicted that there would be 2.9 billion passenger journeys during that year's Chunyun season. It has been called the largest annual human migration in the world (Wkipedia).
https://en.m.wikipedia.org/wiki/Chunyun#/media/File%3AAnnual_human_migration_world_map.svg
