(quick & simple guide)
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 script.
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 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.
Stay safe - If something smells fishy, don't open it, don't fill the form, don't download.