What is a complaint? Matt Owen 04 October 2023 09:17 Updated A complaint is when someone says they're not happy with a service they've been provided by an organisation, for example, if they've lost out on money or been inconvenienced due to a bad service. Related articles What can I complain about? How do I make a complaint? What benefits does Onsi offer? What is included in 'Wellbeing'? How will my complaint be handled?