An HTML5 lesson said something about HTML4, so what is HTML4

Answer 1

the previous version of the actual HTML5. It didn't have many GREAT feature as HTML5 does, as Geolocation API, semantic tags, useful new input types, and much more

Answer 2

The HTML Fudamentals lesson is about version 4 and 5. It's important to have an understanding of the tags from version 4 that are deprecated, and the tags from version 5 that are new. If you find yourself updating an older website you may come across tags that you'll want to update.

Answer 3

So it's was a predecessor to HTML5?

Answer 4

Yes a previous version.