'Ilm al-huruf
ʿIlm al-Ḥurūf or the science of letters, also called Islamic letterism, is a process of Arabic numerology whereby numerical values assigned to Arabic letters are added up to provide total values for words in the Quran, similar to Hebrew gematria. Used to infer meanings and reveal secret or hidden messages.
ʿIlm al-Ḥurūf is composed of the two words ʿilm meaning "knowledge", and ḥurūf, the plural of the word ḥarf, meaning "letters".