Usually, it's the screw loose behind the trigger.
Accuracy is different things to different people.
For instance, accuracy to the bench shooter is different from that the silhouette shooter. The silhouette shooter will have a different definition of accuracy from the BPCR shooter. The BPCR guys definition of accuracy differs significantly from that of the tactical/sniper guys. The sniper guys usually have little in common with the guys with hunting rifles. The hunters definition of accuracy is substantially skewed from the the accuracy defined by most handgunners.
All of the above have nothing in common with shotgun shooters- which all want different things depending upon their selected sport or discipline...except slug shooters.
Heck, I figure that trying to define accuracy among a group of shooters is like trying to ask different religions about their belief systems and compare them.
There is no definitive definition to "accuracy."
However, even though there is no definition of accuracy, anyone can realize when it
isn't there.
We can only define accuracy once we figure out what we want that accuracy to be.