Markup = HTML, XHTML, XML
<p> this is a paragraph of text written in HTML </p>
A. A markup language is a language that annotates text so that the computer can manipulate the text. Most markup languages are human
readable because the annotations are written in a way to distinguish
them from the text.
B. A markup language is a system for annotating a document in a way that is syntactically distinguishable from the text. The idea and
terminology evolved from the "marking up" of paper manuscripts, i.e.,
the revision instructions by editors, traditionally written with a
blue pencil on authors' manuscripts.
Markdown = simplified in the best way WYSIWYG
WYSIWYG = denoting the representation of text on-screen in a form exactly corresponding to its appearance on a printout.
In the past, a WYSIWYG editing tools gave away too much design
control. Someone could unknowingly add a new style to the design (like
red italic bold headers) without meaning to. More often than not, it
was a purposeful design addition, but that inevitably leads to a race
to the bottom, so style treatment became larger, bolder, and brighter.
This makes designers sad :( because their carefully crafted theme gets
lost in the noise.
Bottom line, people who edit content should focus on the words and the
designer should make them pretty. Markdown does an excellent job at
drawing that line in the sand, equipping us to all play nice together.
When a designer pushes a new style to the website, the styles are
consistently reflected across the whole site, so the design stays
fresh and up to date with browser caveats and features.