The grip of a violin bow (or bow of any other stringed instrument) is often mistakenly referred to as the 'frog'.
According to The Oxford Dictionary of Music, The Grove Concise Dictionary of Music, The New Grove Dictionary of Musical Instruments (vol 3, P-Z) and the Collins English Dictionary (3rd. ed.) the frog is in fact the nut in the heel of the bow which tightens the horsehair of the bow.

The reason the heel of the bow is often referred to as the frog is because of the manner in which the musician holds the bow. S/he holds the bow near the frog, and the index and second and third fingers rest on the stick while the thumb presses on the underside of the frog.

(For more info on the violin refer to its node)