Radharani is Krsna's pleasure potency

TODAY IS RADHASTAMI, the appearance day of Srimati Radharani. Fifteen days after Krsna's birth Radharani appeared. Radharani is Krsna's pleasure potency. Radha-krsna-pranaya-vikrtir hladini-saktih. The Supreme Personality of Godhead has varieties of energy, as confirmed in the Vedic literature:parasya saktir vividhaiva sruyate.

A lecture given on Radharani's Appearance Day, in London, September 18, 1969
By A.C. Bhaktivedanta Swami Maharaja