Ma'anar ƙamus na kalmar "kariyar halittu" tana nufin hanyoyin halitta ko na wucin gadi da dabarun da rayayyun halittu suke amfani da su don kare kansu daga cututtuka, cututtuka, ko wasu abubuwan da suka shafi halittu masu cutarwa. Hanyoyin kariyar halittu na iya haɗawa da shingen jiki, kamar fata ko mucous membranes, da kuma martanin biochemical da immunological wanda ke taimakawa jiki ganewa da kawar da ƙwayoyin cuta masu haɗari ko abubuwa masu guba. Misalan tsarin kariyar halittu a cikin mutane sun haɗa da tsarin rigakafi, amsawar kumburi, da tsarin haɗin gwiwa, da sauransu.