A cosmetic typically used by women to redden the cheeks so as to provide a more youthful appearance, and to emphasize the cheekbones.
It's very hard to tell this apart from blush. Generally rouge is drawn more toward the ears while blush is drawn below or closer to the eyes. If a character isn't wearing other types of makeup like lipstick, mascara or eyeshadow then it's probably just an average anime blush and not rouge.
