citations (NAP)

a reference to your business which occurs on another web page, typically including the name, address, and phone number

A mention of your business by name, especially if your address and phone (NAP) are included in the mention.

The Algorithm notices such mentions and values them highly — even if the mention doesn't include a link to your website.

This partly explains why there are uncounted (though perhaps countable) web sites which are little more than an excuse to publish a list of businesses that was scraped from the internet by a web crawler.

If you want a glimpse into this dismal corner of the Internet, Google up a few small businesses in your neighborhood and look at the second page of results, which are mostly Yelpholes.