In the earliest Hebrew inscriptions from the 10th century B.C. no vowels were indicated. Thus the words melek (king), molek (ruling), malak (he ruled), malkah (queen), malaku (they ruled), etc. would all be written simply as mlk. From the ninth to the sixth centuries B.C. (i.e. before the Babylonian Exile which followed the fall of Jerusalem in 587 B.C.), the consonants y, w and h were used at the end of a word to indicate final vowels:
y=i (malki, my king)
w=u (malaku, they ruled)
h= any other final vowel (malkah, queen).
In the post-Exilic period, w and y were used as vowel indicators also inside a word, with slightly different values, although the letter h continued to be used only at the end of a word to represent certain final vowels. The three letters, y, w and h, when used as vowel indicators, are called matres lectionis (literally in Latin, “mothers of reading”) in traditional Hebrew grammatical terminology.
During the ninth and tenth centuries A.D. in the city of Tiberius, Jewish scholars, called Masoretes or traditionalists, perfected a system of vowel notation which was added to the earlier crude system of matres lectionis in order to indicate proper vocalization. Using the Masoretic symbols (mainly dots in various numbers and positions next to consonants) a large number of new combinations were created, among them holem (pronounced “oh”) and Shureq (pronounced “oo”).
In later use the matres lectionis were sometimes dropped from the inside of words where they had been used in combination with the Masoretic vowel indicators. This shorter spelling of words is called “defective.”