What Is Applied Category Theory?

Has been discussed previously[1] on HN, but it's been a while. And my interest in this was piqued by this recent(ish) video series on "Category Theory for AI".[2]

I was a little taken aback when I first heard them use the term "applied" in conjunction with the term "category theory" since you hear so much rhetoric on the 'net about how category theory is "abstract nonsense" or whatever. You see a few claims that it's only really of interest to pure mathematicians. But maybe that's not the case after all? Hmmm. I feel like I have some reading and watching to do.

[1]: https://hn.algolia.com/?query=What%20Is%20Applied%20Category...

[2]: https://www.youtube.com/playlist?list=PLSdFiFTAI4sQ0Rg4BIZcN...