What’s a Period Data Type and Why do I Care?
More than likely, you need to keep track of the beginning and ending of some kind of an event. Maybe you track how long employees have been with your company, how much time users spend on a particular web site, or the duration of insurance policies.
In other words, you need to track temporal data. And you probably use a couple of DATE or TIME or TIMESTAMP columns to do just that.
Consider the following employee table that tracks the job duration of employees by using two DATE columns: start_date and end_date.