Definition of roundels:
(n) :
Anything having a round form; a round figure; a circle.
(n) :
(aviation) A circular insignia painted on an aircraft to identify its nationality or service.
(n) :
A small circular shield, sometimes not more than a foot in diameter, used by soldiers in the fourteenth and fifteenth centuries.
(n) :
(heraldry) A circular spot; a charge in the form of a small coloured circle.
(n) :
(music) A roundelay or rondelay.
(n) :
A bastion of a circular form.