Often your company or website will be mentioned on another website without a backlink to your page. It's really useful to have visibility of these type of mentions as you can contact the site owner or publisher to see if they can update their post to include a link (ideally with decent anchor text to a page within your site).
Citations are also known to be a ranking factor, with a strong emphasis for local search.
Click optimise to see a table containing links to web pages where your URL is referenced on the page but there is no clickable link for users and search engines to follow to your site.