Short definition
A citation is any online mention of a business's name, address, and phone number, typically on directories, social profiles, and industry sites.
In depth
Citations are votes of legitimacy for a local business. Google evaluates how many credible directories list the business and whether the NAP matches across them. Structured citations live on directory sites with a defined format (Yelp, Apple Maps, BBB, Angi). Unstructured citations are mentions in articles, blog posts, or news stories. Both count; consistency matters more than volume after a baseline of ~50 quality structured citations is reached.
Example
A new HVAC company builds 60 NAP-consistent citations on tier-1 and industry directories, then watches map-pack ranking climb from page 3 to position 2 in 90 days.