what are the retro tab things that show up on many websites ?

They often look like pixelated squares, show up in the same place and say things like, “Ambassador of friendship” or “don’t be a toad, reload”. Im assuming they came from a much earlier version of the internet. I’m younger and completely new to HTML so it might sound like a dumb question but I want to know what they are exactly or get a keyword so I can look it up and find out more https://19216801.onl/ . Thanks.