What does it mean by "3 Month Paternity Relief Contract"?

Paternity leave is time taken off by a new father to care for his child. The equivalent for a new mother is maternity leave. Most countries have a law which mandates that employers must give new parents time off. To cover their absence, short-term contracts are often offered.

In this case, it appears the job advertised is to cover a three-month period of paternity leave. This would be a temporary contract. This may be unsuitable if you are looking for a permanent position. However, some employers may consider hiring someone who has filled in for a person on parental leave if they do a good job and they have vacancies, it may be worth asking if this is possible.