The definition of 9 to 5, a nine to five is a normal and routine job.
The term 9 to 5 workday was introduced by the Ford Motor Company in the 1920s, it later became standardized by the Fair Labor Standards Act in 1938, as a way of trying to curb the exploitation of factory workers.
The definition of nine to five is the normal work schedule for most jobs in the U.S.. The term is often used to describe boring or unfulfilling jobs.
The schedule changes based on countries, especially in Europe, where they tend to often have a pause around noon and end later, or start earlier.