Step 1: Definition.
Section 2(oo) of Industrial Disputes Act defines retrenchment as termination of service by the employer for any reason whatsoever, other than as punishment, except in cases like voluntary retirement, superannuation, or termination on ground of continued ill-health.
Step 2: Clarification.
Termination due to ill-health is included, whereas abandonment or superannuation are not retrenchment.
Step 3: Conclusion.
Thus, option (a) is correct.