Definition: To move or be hurled quickly through the air.
There are several signs for "FLY" depending on what the subject/object is in a sentence. Some are classifier verbs such as "travel by airplane" and "flying kite".
To make (something) float or move through the air. E.g. flying kite, flying bird in the sky, insect flying around.
Not all classifier verbs and plain verbs can work with FLY verbs. So, the pathline classifier (video right above) is used. E.g. BIRD FLY-WINGS CL:pathline(in the sky). You cannot use the FLY-WINGS sign in the air above you. Instead, use the classifier pathline.