Hypertext Mark-Up Language. Or simply "text with formatting". For example, to define a paragraph in HTML: <p>This is a SENTENCE!</p>
HTML is "plain text with formatting".
HTML is not an application, it is not an executable on a computer.
HTML cannot change the system settings, cannot access files.
No direct ways to "infect" a computer, thus cannot contain a virus.
HTML is technically safe, but still can be misused in many ways.
E.G. Websites that look like legit banks, asking for login/password.
E.G. Websites that prompt for "an update", but downloads a virus instead.