Ma'anar ƙamus na "Siffa ta farko ta jima'i" tana nufin halaye na zahiri da na halitta waɗanda ke da hannu kai tsaye a cikin haifuwa ta jima'i da kuma bambance-bambancen tsakanin jikin namiji da mace. Wadannan sun hada da gabobin haihuwa, irin su ovaries, mahaifa, da farji a cikin mata, da tes, prostate gland, da azzakari a cikin maza. Abubuwan halayen jima'i na farko suna tasowa a lokacin balaga kuma suna da alhakin samar da gametes (kwayoyin jima'i) da kuma ikon yin jima'i.