To fondle with a womens breasts to have her nips become hard and firm. Usually as a prelude to sex. Manipulation of the nipples; or, Nipulation in order to highten sexual awareness.
Stop nipulating me, your not getting it tonight; I have a headache!
Honey, I am going to Nipulate you into orgasam...
Nipulation is not a pre-requisit to sex, however, it does make it much more pleasurable for the woman.