A voluntary payment given to a person for services delivered. These are generally acts or services for which customs and traditions disallow a price to be set. Payments are made just as a gesture to thank or appreciate the person for rendering the services. The honorarium is not legally required.
A person was told to judge a competition for which the sponsors were only willing to offer an honorarium, so, legally there is no payment to be made for this task. There is no salary, it is not a freelance or an hourly contract.
Another example of an honorarium could be a situation where a person gives a speech at a conference, he/she may receive an honorarium for the service.