WYSIWYG
“What You See Is What You Get.”
WYSIWYG describes editors, such as word processors and webmail, that show you the formatted result as you type and hide the underlying markup. This makes simple tasks like writing an email easier, but can make complex documents like bulletins and newsletters harder to control precisely.
For example, when writing an email you probably have toolbar buttons for italics and bold. You cannot see where the editor places the invisible markers that start and stop the formatting. Many editors also have a button to switch to HTML (source) editing. You give up the convenience of having the tags inserted for you, but gain direct control over exactly how the text is formatted.
WYSIWYG
This is italics and this is bold.
HTML<p>This is <em>italics</em> and this is <strong>bold</strong>.</p>
Editing at the source level has many advantages, and much of the work in the office is done in markup languages such as Markdown, HTML, and LaTeX. Why?
Take this website as an example. It could have been built with WordPress, but WordPress carries significant overhead: hosting fees, server resources to run a database that a simple site does not need, cPanel, complicated theming, and a steady stream of security patches. Instead, this site is written in Markdown, converted to static HTML and CSS by Hugo, stored in a GitLab repository, and published automatically. This requires basic familiarity with HTML, the command line, and Git, but eliminates all of those administrative burdens: there is no database, no server-side code, and nothing to patch.
A more everyday example is formatting a document in a WYSIWYG word processor like Microsoft Word. Have you ever pressed Tab to indent one line, only to have the entire paragraph move? LaTeX has a significant learning curve, but it does not produce surprises like this: the output matches exactly what you wrote.