HTML stands for Hypertext Markup Language.
It was invented in 1991 by Tim Berners-Lee while he was working at CERN. He created it as a way to structure, interlink, and share documents across the newly formed World Wide Web.
He based it on an in-house documentation format called CERN SGML (or SGMLguid), where the acronym meant Standard Generalized Markup Language and guid was for some reason a shortening of guide. Tim’s original publication only had 18 tags!