Best translation is, I think, "partially full." He's essentially looking for 3-star cards that need only 1-2 games in the lost warehouse to jump to 4-star or 4-star cards that need a game or two to go to 5-stars. Why? Because it's a cheap way to get lots of experience quickly and jump up in level.
You can make a pretty good return buying low level copies of cheap 5* cards like Phonos and selling them to people looking for pful cards, in raw % terms, although the time-value of the clintz is much more questionable ...
Those are not bad deals the 3* price is a little cheap but the 4* price is good compared to other buyers
@Mr_Valy-evo do you buy 5* Pfulls and if so how much do you pay for them please send me a private message with your answer thanks.