Chudan Oyayubi Ipponken is a technique in Kyokushin karate. It translates to 'Middle-Level Thumb One-Knuckle Fist.' This technique involves forming a fist where the thumb presses against the base of the index finger, creating a single-knuckle striking surface. The term 'Chudan' refers to the middle level, 'Oyayubi' indicates thumb, 'Ipponken' denotes one-knuckle fist. It is commonly used for close-range strikes to vulnerable areas such as the solar plexus, ribs, or abdomen.