YOONYUL is a nickname for two of the girls who are members of So Nyeo Shi Dae or Girls Generation, whose names are YOONA and YURI and who treat each other like sisters. They even look alike.
YOONA: Yoon and YURI: Yul = Yoonyul
So Nyeo Shi Dae, SNSD, or Girls Generation is a nine member girl's Pop Music group from South Korea.
No, Yoona and Yuri aren't sisters. They are very good friends and share quite a bit in common. This may be the reason why they are sometimes mistaken for sisters.
TaeSica [Taeyeon & Jessica] SunYeon/TaeSun [Sunny & Taeyeon] HyoSica [Hyoyeon & Jessica] HyoYoung [Hyoyeon & Sooyoung] HyoSun [Hyoyeon and Sunny] HyoTae [Hyoyeon & Taeyeon] HyoFany[Hyoyeon & Tiffany] HyoRi[Hyoyeon & Yuri] JeNy[Jessica & Tiffany] SeoSica/JessHyun[Seohyun & Jessica] SeoFany[Seohyun & Tiffany] SeoRi [Seohyun & Yuri] SooHyun[Sooyoung & Seohyun] SooSica [Sooyoung & Jessica] SooSun [Sooyoung & Sunny] SooTae [Sooyoung and Taeyeon] SooFany [Sooyoung & Tiffany] Soori [Sooyoung & Yuri] SunFany [Sunny & Tiffany] SunSica[Sunny & Jessica] SunHyun [Sunny & SeoHyun] SunYeon [Sunny and Taeyeon] SunRi [Sunny&Yuri] SeoTae[Taeyeon & Seohyun] TaeFany [Taeyeon & Tiffany] TaeYoon [Taeyeon & Yoona] TaeRi [Taeyeon and Yuri] TiRi [Tiffany & Yuri] YoonHyo [Yoona & Hyoyeon] YoonSica [Yoona & Jessica] YoonHyun[Yoona & Seohyun] Soona [Yoona & Sooyoung] YoonSun[Yoona & Sunny] YoonFany[Yoona & Tiffany] YoonRi/YoonYul[Yoona & Yuri] ALL the credits to Soshified.
No, Yoona and Yuri aren't sisters. They are very good friends and share quite a bit in common. This may be the reason why they are sometimes mistaken for sisters.
TaeSica [Taeyeon & Jessica] SunYeon/TaeSun [Sunny & Taeyeon] HyoSica [Hyoyeon & Jessica] HyoYoung [Hyoyeon & Sooyoung] HyoSun [Hyoyeon and Sunny] HyoTae [Hyoyeon & Taeyeon] HyoFany[Hyoyeon & Tiffany] HyoRi[Hyoyeon & Yuri] JeNy[Jessica & Tiffany] SeoSica/JessHyun[Seohyun & Jessica] SeoFany[Seohyun & Tiffany] SeoRi [Seohyun & Yuri] SooHyun[Sooyoung & Seohyun] SooSica [Sooyoung & Jessica] SooSun [Sooyoung & Sunny] SooTae [Sooyoung and Taeyeon] SooFany [Sooyoung & Tiffany] Soori [Sooyoung & Yuri] SunFany [Sunny & Tiffany] SunSica[Sunny & Jessica] SunHyun [Sunny & SeoHyun] SunYeon [Sunny and Taeyeon] SunRi [Sunny&Yuri] SeoTae[Taeyeon & Seohyun] TaeFany [Taeyeon & Tiffany] TaeYoon [Taeyeon & Yoona] TaeRi [Taeyeon and Yuri] TiRi [Tiffany & Yuri] YoonHyo [Yoona & Hyoyeon] YoonSica [Yoona & Jessica] YoonHyun[Yoona & Seohyun] Soona [Yoona & Sooyoung] YoonSun[Yoona & Sunny] YoonFany[Yoona & Tiffany] YoonRi/YoonYul[Yoona & Yuri] ALL the credits to Soshified.