Flicker is the image failing to arrive intact and on time. The signal chain runs from the graphics hardware, through a driver, along a cable, into the display's own electronics.
Cable faults produce intermittent flicker that changes when you move the cable, and often appear as brief black frames rather than dimming.
Refresh-rate mismatches cause steady rhythmic flicker, especially when a display is set beyond what the cable standard can carry at that resolution.
Driver faults tend to flicker only in specific situations — when a video plays, when a game starts, or when the machine switches between integrated and dedicated graphics.