Mater lectionis

In the spelling of Arabic and some other Semitic languages, matres lectionis (/ˈmeɪtriːz lɛktiˈoʊnᵻs/; from Latin "mothers of reading", singular form: mater lectionis, Hebrew: אֵם קְרִיאָה 'em k'ri'á), refers to the use of certain consonants to indicate a vowel. In Arabic, the matres lectionis (though they are much less often referred to thus) are alif ا, waw و, and ya' ي. The letters that do this in Hebrew are א aleph, ה he, ו waw (or vav) and י yod (or yud). The yod and waw in particular are more often vowels than they are consonants.