Uki otoshi (floating drop) is one of the traditional forty throws of Judo as developed by Jigoro Kano. It belongs to the fourth group, Dai Yonkyo, of the traditional throwing list, Gokyo-no-Nagewaza, of Kodokan Judo. It is also part of the current 67 Throws of Kodokan Judo. 
Uki otoshi is a pure te waza, with the pullig hand lifting up and pulling the uke to their front. The lifting hand drives up and again to uke’s front. Tori then drops to one knee, getting out of the way of uke’s momentum. As they drop, the lifting hand continues to drive uke forward as the pulling hand makes a quick circular movement and changes direction, whipping uke over. The dropping movement ensures that uke is thrown.
Uki otoshi features regularly in Kata, the first technique in Nage-no-kata, countered by Tai otoshi in Nage-waza-ura-no-kata and as a counter to Uchi mata in Kaeshi kata. 
From Wikipedia  and Akitas Judo