For example, you use Google Fonts. For that you need to load CSS. So that's three roundtrips for rendering your page: 1) your page, 2) the Google Fonts CSS, 3) the font files.
We've build a WordPress plugin called PhastPress (fast press) that helps you reduce the request count and those roundtrips without building your own theme. https://wordpress.org/plugins/phastpress/
Among other things, it inlines the critical CSS needed for rendering the page, defers all script loads, and optimizes images. Cuts page size by ½ on the stock theme, and the amount of additional roundtrips to 0.
Well, before we get to the Google Fonts CSS, we first have to open another connection there, do a TLS handshake, and maybe we even need to look that host up first before any of that.
The one "logical" roundtrip (an additional request) would indeed count for many if you consider DNS, TCP and TLS handshakes.
Even more of a reason to get rid of them.