What does fun run mean?

People in fun run refer to people who study, work or do activities at night. This word comes from the description of evening self-study in traditional education in China. In ancient times, many students or scholars often chose to study at night in order to study better or prepare for exams. These people usually stay up late to study or prepare for exams, so they are called fun run. In modern society, people in fun run can also refer to people who work at night, such as night workers and white-collar workers who work overtime. They are usually people who work hard at night to complete work tasks or pursue personal goals.