A dofollow link is an ordinary link with no rel="nofollow", rel="sponsored" or rel="ugc" attribute. Search engines follow it and count it as a recommendation of the page it points to.
There is no dofollow attribute. Every link is followed unless it is marked otherwise, so "dofollow" is just the name people give to a link that was left unmarked.
Sites that accept submissions from anyone often mark outgoing links nofollow by default and give a followed link only to products they have checked, or to makers who link back.
Why it matters for a launch
Dofollow links are the ones that help a new site rank. On IndieLaunch, a free launch gets a dofollow link once the maker adds the IndieLaunch badge to their site, and a Premium launch always has one.
Read more: Free dofollow backlinks for a new site