Effective Date is the date when a row/data/info become effective.
E.g.
A employee Mary was hired on 19 Feb 2010. The effective date is 19 Feb 2010.
Mary was promoted to Sales Manager on 1 June 2010. The effective date is 1 June 2010.
Effective Date conflicts:
The firm create a new position and set the effective data on 1 Jan 2010. You cannot assign this position to any employee with an effective date before 1 Jan 2010.