"Dofollow" isn't an HTML attribute. It's shorthand for a link that has no rel="nofollow", rel="sponsored", or rel="ugc" value. Search engines treat it as an editorial vote for the destination page.
Because these links can pass link equity, they're the ones most site owners want from directories, guest posts, and partner pages.
Why it matters when you launch
When you pick launch directories, check whether the listing link is dofollow. A dofollow listing on a high-authority directory is a real backlink; a nofollow one mainly sends referral traffic.