Headless means that you're using e-commerce platform only via API and build your front-end in whatever tech you want (next, nuxt, Remix, etc). It's different from a traditional approach when e-commerce platform handles front-end (HTML templates rendering). In Shopify can do both.
Funny that headless is now considered "traditional," when that was considered standard for a decade and a half. Relying on the platform was considered amateur.
"Traditional" is just another way to say "what was once the norm", so your comment is a bit pleonastic.
Is relying on the platform no longer considered amateur? If yes, call me old fashioned, because I've never liked those platforms...
https://www.shopify.com/enterprise/headless-commerce