Pulling such a specific term shows that you probably already know the answer. That's not a term that most business owners and for that matter, it's not a term that's actively used in the SEO industry as a whole.
What does it mean? It basically means that if there are two or more links to the same page, on a page, then Google only cares about the anchor text of the first link.
This is REALLY old-school thinking though.. I mean it's 10+ years old. It still holds some weight, but if you're going to be thinking about first link priority, you may as well throw in Keyword Density and Page Rank and other factors from years ago that no longer play a role in ranking.
Links should be athority sites, PA / DA means Page Athority / Domain Authority respectively, so the both factors are important, and Relevancy is also one of the main factor in link building activity