If you're referring to when reviewers describe a deck that way, I pretty much ignore that pronouncement in a review. A deck has to be readable to me, so someone else's opinion on how well a deck reads for them is a moot point, especially since most of those reviews seem to base readability on how well traditional symbolism is depicted. I read intuitively, always, so I don't pay attention to what any symbols or numbers are "supposed to" mean. Therefore, for me, a deck is more readable if it has a lot of strong and/or interesting imagery and strays as far from RWS as possible. I can read with traditional decks, but it's just not as enjoyable for me to do so. So, I prefer non-traditional. Plus, for me to use my intuition and not rely on the expected recipe for numbers in the suits, the minor arcana needs imagery. Can't read just pips. Well, I know I'm not the typical tarot reader, but that's what readability means for me.