<var>
A variable: unknown, parameter, placeholder.
It works for the unknown in an equation, for the name of a function parameter and for the variable part of a terminal command — the bit the reader is meant to replace with their own value.
It renders in italics by default, which gets it confused with <em>. The difference is that <var> carries no emphasis at all.
<p>
Run <code>python3 build.py <var>destination</var></code>
to write the site somewhere else.
</p>