Good Cause
The exact meaning of good cause varies from state to state, but generally it means what it says: You must have a "good," meaning legitimate, reason for firing the employee. Usually that means the termination must be based on reasons related to business needs and goals. Firing an employee because you don't like the fact that she has an illegitimate child, for example, isn't good cause. Firing an employee because he harasses female coworkers is.
Examples of good cause include the following: