We have 2 types of holds with deprecated variants that I won’t go into.
These types are simply Holds and Rolls. Rolls are not to be confused with the pattern known as a roll.
Holds you have to hold. You have a window to regrab them if you release them which depends on your judge window.
Rolls you have to tap. The window to keep tapping before they drop completely is about the same as the hold regrab window.
NG means you dropped a hold or roll. It basically stands for Not Good, similar to how completing a hold or roll used to say OK. These visuals were removed from the game a while back because they were adding a lot of visual noise to gameplay, and the only evidence of them existing now are the NG and OK counts.