1- WHAT IS FIXED SALARY?
When an employee gets his/her full salary even if he/she has compassionate leave (because of sickness or other reasons), his/her salary will be regarded as fixed monthly salary.

2- WHAT IS THE NETTING OF FIXED MONTHLY SALARY AND BENEFIT FOR TEMPORARY INCAPACITY RECEIVED BY EMPLOYEES WHO GET FULL SALARY EVEN IF THEY ARE SICK OR ON LEAVE?
Employee, who gets benefit for temporary incapacity because of medical report, may get fixed monthly salary by giving back those benefits to his/her work place.

Source: SSI