In other words, "popular". And thus the inevitable problem with using notability as a guideline.
Once that becomes the principle inclusion/exclusion criteria (as it tends to be in most of the discussion in AfD), exclude lots of junk, but you also only include things that are so common that everybody already knows about them anyway -- thus making an encyclopedia as the "place you go to look up stuff you don't know" moot.
This creates an irrational fear of including non-notable "false positives" (when bits are effectively free), and excluding perfectly good information that falls beneath some particular editor's personal interest radar.
Once that becomes the principle inclusion/exclusion criteria (as it tends to be in most of the discussion in AfD), exclude lots of junk, but you also only include things that are so common that everybody already knows about them anyway -- thus making an encyclopedia as the "place you go to look up stuff you don't know" moot.
This creates an irrational fear of including non-notable "false positives" (when bits are effectively free), and excluding perfectly good information that falls beneath some particular editor's personal interest radar.