Great question — answering as the UphillTech team:
You are going to hear the term citation used in different ways from SEOs and even Google. Please do not get confused. The best way to understand what is happening in search is to look at the history. I will not get into details, however, I will mention originally, links were links and citations were simply mentions. So what does that mean? Before schema.org, before Author Rank, before almost anything we knew that tried to match duplicate content, Google had a series of filters that the index engine used to recognize various content elements such as author name, post dates, company names and locations, etc. These data elements were put into the knowledge graph. This is just one example....
Full answer by closetnoc: https://webmasters.stackexchange.com/a/128131 (CC BY-SA 4.0).
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