The sleeper tag is one that can be applied to any player, depending on the context of how that player might be “sleeping”. I wrote earlier this month about what constitutes a sleeper for these Saturday articles. For me, it’s largely a prospect who falls outside of the top 30, though that isn’t universal.
Not everyone follows the minor league system. There are a large majority of Pittsburgh Pirates fans, and fans of every other Major League team, who can’t name a single prospect. They couldn’t even do it before Paul Skenes arrived in the majors.