Backlinks are incoming (external) links to a website or web page, other than your own.
These external links are not to the internal link pages of the same website.
The more your website (link) is mentioned in other websites, search engines would regard that website must be popular.
Clients used to ask "How Many Backlinks Do I Need?"
Well, there is no absolute answer to that.
Actually as many as possible to out-number your competitor.
The mentioned your website in other places, the better you are in terms of online presence and ultimately website ranking in search engines.