Text overlay in articles?

I want to have a feature on my WordPress blog (which I create also with Elementor) where I can highlight some words/phrases in an article and the visitor can see extra explanations just by going over this text part with its mouse. Similar like on this page.

I don’t know how this is called and maybe that’s why I cannot find how to do it. Any ideas?

The page I need help with: [log in to see the link]