Ma'anar ƙamus na parasitism wani nau'in alakar alama ce tsakanin kwayoyin halitta guda biyu inda ɗayan kwayoyin halitta, wanda ake kira parasite, ke amfana a kashe ɗayan kwayoyin halitta, wanda ake kira mai gida. Kwayar cuta takan rayu a ciki ko akan mai gida kuma tana ciyar da ita, sau da yawa tana haifar da cuta ko cuta. Mai gida yana yawanci rauni ta hanyar alakar parasitic, amma maiyuwa ba lallai bane ya mutu sakamakon haka. Wannan alakar ta kasance mai gefe guda, tare da fa'idar parasite na mai gida. Misalai na parasitism a cikin duniyar halitta sun haɗa da ƙuma akan karnuka, kaska a kan barewa, da tsutsotsi a cikin hanjin ɗan adam.