Unugyada dhiiga-cad waa unugyo ka tirsan nidaamka difaaca jirka, kuwaas oo ka hortaga caabuqa, difaac-kiciyeyaasha (antigens), iyo unugyada is-bedelay. Waxay muhiim u yihiin difaaca dabiiciga ah (innate immunity) iyo difaaca la-qabsiga ah (adaptive immunity).