Ma'anar ƙamus na "ƙungiyar jini" tana nufin rarrabuwar jini bisa ga kasancewar ko rashin wasu alamomi (antigens) a saman jan ƙwayoyin jini, waɗanda ke ƙayyadaddun dacewa ga ƙarin jini kuma yana iya nuna wasu halaye na kwayoyin halitta. ko predispositions zuwa wasu cututtuka. Rukunin jini guda huɗu sune A, B, AB, da O, waɗanda aka ƙara bambanta su da kasancewar Rh factor (positive ko negative).