bino is the superpartner of the gauge boson corresponding to weak hypercharge. It mixes with one of the gauginos corresponding to weak isospin to give the photino and the zino.
Gauginos mix with higgsinos to form linear combinations ("mass eigenstates") called neutralinos (neutral) and charginos (charged). Since (in many models) the lighest neutralino is stable, it is a WIMP and a candidate for dark matter.