To greed is to delay the safe option in order to gain more. The clearest example is holding a pallet: instead of dropping it as soon as the killer approaches, the survivor takes another lap around the tile first, hoping to buy time without spending the resource.
Greeding is how good survivors extend chases far beyond what the map should allow, and it is also how they lose them. The line between "one more loop" and "hit taken" is small and depends on exactly how the killer is approaching.
In a timed duel, greeding is directly rewarded. There is no team to protect and no objective to get back to, so the only currency is seconds - which makes the risk mathematically worth taking far more often than it would be in a normal match.