Plain English Meaning
The colored bands and lines painted on the airspeed dial that tell the pilot at a glance which speeds are safe, which require caution, and which must never be exceeded.
Full Definition
Color-coded arcs and lines on the face of the airspeed indicator that show the operating speed ranges and limits for the aircraft. The standard markings are: a white arc (flap operating range, from stall speed with flaps extended at maximum landing weight up to maximum flap extended speed), a green arc (normal operating range, from stall speed with flaps retracted up to ), a (, to be flown only in smooth ), and a (, ).