For purposes of sections 79-1234 to 79-1239, unless the context otherwise requires:

(1) Board means the governing board of any educational service unit;

(2) Certificated employee means any teacher, nurse, or other person required to have a certificate from the State Department of Education who is employed by an educational service unit;

(3) Just cause means incompetency, neglect of duty, unprofessional conduct, insubordination, immorality, physical or mental incapacity, or other conduct which interferes substantially with the continued performance of duties or a change in circumstances such as financial exigency or a diminution of demand for services by the school districts served by the educational service unit necessitating a reduction in the number of teachers or nurses to be employed by the board;

(4) Permanent certificated employee means a certificated employee (a) who has served under a contract with the educational service unit for at least three successive years under any contract which was entered into to create initial employment on or after September 1, 1986, or (b) who was initially employed by the educational service unit prior to September 1, 1986; and

(5) Probationary certificated employee means a certificated employee who has served under a contract with the educational service unit for less than three successive years under any contract which was entered into to create initial employment on or after September 1, 1986.