Short answer
A local citation is an online reference to a business. It commonly includes the business name, address, and phone number, but may also include a website, hours, categories, photos, services, and other profile details.
A simple example
A directory profile that lists “Acme Plumbing,” its street address, phone number, website, service category, and opening hours is a structured citation. A local newspaper article mentioning the business name and city is an unstructured citation.
Citations are not the same as links
A citation can contain a backlink, but it does not need one to be a citation. The core idea is the business mention and identifying data, not the presence of a clickable link.
What to do next
If you are working on citations for a real business, create one canonical record for the business first. Then audit current listings before deciding what needs to be corrected or added.