English Translation
What is Koinobori?
こいのぼり(鯉のぼり, 鯉幟, Koinobori), meaning ‘carp streamer’ in Japanese, are carp-shaped windsocks traditionally flown in Japan to celebrate Tango no sekku (端午の節句), a traditional calendrical event which is now designated as Children’s Day (子供の日, Kodomo no hi), a national holiday in Japan.
From Wikipedia.