Hebrew spelling refers to the way words are spelled in the Hebrew language. The Hebrew alphabet contains 22 letters, all of which are primarily consonants. This is because the Hebrew script is an abjad, that is, its letters indicate consonants, not vowels or syllables. An early system to overcome this, still used today, is matres lectionis, where four of these letters, alef, he, vav and yud also serve as vowel letters. Later, a system of vowel points to indicate vowels (Hebrew diacritics), called niqqud, was developed.