HTML

html iconHTML (HyperText Markup Language) is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS)…

Wikipedia.

It is the code behind whatever you see on a website. You may use html in the post editor in Glow Blogs by selecting the Text tab at the top of the editor. It may on occasion be helpful in cleaning up text or adding features that are not supported by the editor. It may also be of use to students learning html.

Gif of toggleing between Visual and Text Editor