Answer By Dr Zakir Naik,The word Fidia means the compensation for a fast which could not be kept due to some permanent disability or some disease as the Qur'an mentions in Surah Baqarah ch. no. 2 verse no. 184 that "If it's difficult for a person to fast then he can feed one indigent person, one poor person."So if a person who has permanent disability, he is permanently sick or he is very old and can't fast then he should feed one poor person for every fast he has missed and this is called as Fidia