What does headless means in software?

loads page

first thing I see is full-screen popover with client testimonial

second thing I see is fixed-position nav at top, fixed-position cookie notice, and fixed-position bubble of some guy's head in the lower right of the screen

sees "ad" in URL

starts to suspect this is a shit site that's more focused on analytics than useful info

leaves

Note that your website doesn't have a scrollbar, which is terrible for UX.