Boss' Day is a celebrated on October 16th unless it falls on a weekend day and is then celebrated on the work day closest to October 16.
On this day people take opportunity to tell their bosses what they really think of them, but also to show their appreciation for those in supervisory roles. It is common to give small presents, cards and flowers.
The tradition was started in 1958 by Patricia Haroski who was working for her father at State Farm Insurance Company in Deerfield. She wanted people to recognize their supervisors and appreciate often challenging positions they are in. She chose October 16 as this was her father's birthday.