Hardship allowance is an allowance type where the employee is required to undertake tasks outside of normal/standard scope.

This is highly variable meaning. Some examples of hardship allowance:
1) OT performed in a roles that does not have normal OT (year end financial closing)

2) Onsite work outside of office hours

3) Abnormal working condition (offshore/construction site/factory/outdoors)

It is not an allowance of people who have hardship (owe ahlong, medical condition, family problem).