The phrase "bat wings" refers to loose and sagging skin on a person's upper arms, resembling the wings of a bat, due to weight loss or aging. Full definition
The top has a concealed button stand and gathered bat wing sleeves. (religionclothing.com)
Draw a single bat wing onto a sheet of black card and cut out. (idealhome.co.uk)
Among the biggest surprises in store for the researchers was how bat wings manipulated the wing motion with correct timing to maximize the forces generated by the wing. (sciencedaily.com)