«الحرام: ضد الحلال، وهو ما طلب ترك فعله بدليل قطعي لا شبهة فيه»
Haram is the opposite of lawful; it is conduct that must be avoided on the basis of conclusive evidence without relevant uncertainty.
The textbook mentions illicit sexual intercourse and theft as examples. The definition depends not on the severity of a label alone, but on the decisive proof establishing an obligation to refrain.
Fard concerns a decisively established duty to do something; haram concerns a decisively established duty to refrain.