Our HOWTOs are released in various formats: Plain Text, HTML, PostScript, and PDF. Instead of having to write the same HOWTO in all of these formats we write just one HOWTO in a source format which gets converted by computer into all of the others.
To get an idea of what this format looks like, take a look at the source file of a webpage (if you haven't already). You will see all sorts of words in <angle brackets>. These are called tags. The webpages use html: Hypertext Markup Language. The LDP uses something like this for its documents. It's called sgml: Standard Generalized Markup Language. But there are various flavors of sgml. The original sgml used by the LDP was called the LinuxDoc flavor. Now many have gone to a more advanced and complicated flavor called DocBook or to an XML (no longer sgml) type of Docbook.
This mini-HOWTO is all about using the simple LinuxDoc flavor of sgml. You may call it "LinuxDoc markup". It can be machine converted to html, plain text, postscript, pdf, and DocBook. It's a lot easier than html or DocBook and you don't need a special editor for it as it's easy to type in the tags (or use macros for them).