Ma'anar ƙamus na kalmar "hadi" shine tsarin da kwayar halittar namiji (sperm) ta haɗu da kwayar halitta ta mace (ovum) don samar da zygote, wanda a ƙarshe zai zama amfrayo. Wannan tsari yana da mahimmanci don haifuwa ta jima'i a cikin tsire-tsire da dabbobi. A cikin tsire-tsire, hadi na iya faruwa ta hanyar pollination na kai ko giciye-pollination, yayin da a cikin dabbobi, yawanci yana faruwa ta hanyar jima'i. Kalmar “hadi” kuma na iya komawa ga ƙarin sinadirai ko sinadarai a cikin ƙasa don haɓaka haifuwarta don tsiron tsiro.