What exactly is a pingback?

So I have a website with 15 articles that I'm trying to rank and I was testing a new strategy, I made 1 wordpress site to 5 articles with a related article + a link to my the article on my website.

I did some backlinking etc etc.

However I checked my website and I noticed that on the bottom of my website there was something called "PingBack" linking to each of the wordpress sites I made depending on the article, how was it added there automatically even though the wordpress sites I made have nothing to do with my website?