Ta'addanci (da turanci Terrorism) shine, yin amfani da tada hankali ko kawo rikici ba tare da yin tunani ba, ko nuna ban-banci akan wanda zai shafa ba, da gangar domin sanya tsoro da tashin hankali a cikin ƙirazan mutane; da tsoratar dasu ko wani sa'in halakar dasu dan cimma burin siyasa ko addini. Ana amfani da wannan ma'anar dan nuna kawo tashin hankali lokacin zaman lafiya ko yin yaƙi da non-combatants. Kalmar "mai ta'adi" da "ta'addanci" ya samo asali ne lokacin French Revolution da ya faru a ƙarshen ƙarni na 18th amma kalmar tayi tashe a bakunan jama'a ne a shekarar 1970 a cikin rahotannin masu yaɗa labarai da littafan dake bayyana faɗace-faɗacen ƙasar Arewacin Ireland, da ƙasar Basque da Palestine. Da ƙaruwar samun yin laifukan kisan kai daga 1980 zuwa abinda yayi sama, haka harin ranar Satumba ta 11 a birnin New York da Washington, D.C. a 2001 ya nuna tabbacin lallai akwai ta'addanci. Babu cikakken ma'anar "ta'addanci" da kowa ya yarda dashi.