Ma'anar ƙamus na "mai kisan kai" shine wanda ya yi jerin kisan kai da gangan da gangan na wani lokaci, yawanci tare da lokacin sanyi tsakanin kowane kisan kai. Irin wannan kisa kuma ana kiransa da serial killer. Dalilai da hanyoyin masu kisan gilla na iya bambanta sosai, amma galibi suna da alaƙa da halaye iri ɗaya kamar sha'awar mulki da iko, rashin tausayi ga waɗanda abin ya shafa, da kuma halin kai hari ga mutane masu rauni.