In ancient Hebrew, there were no vowels but only consonants. In the Dead Sea scrolls, the tetragrammaton is given without vowels. In Middle Ages, a group of Jewish scholars called the Masorites vowelized the Hebrew scripture. In the case of the tetragrammaton, the Masoretic text intentionally misrepresents pronunciation so as to prevent the Lord's name from being use sacrilegiously. Modern scholars have reconstructed the original pronunciation as "Yahweh."
The word "tetragrammaton" is from a Greek word meaning "consisting of four letters." The four letters are yod (י), he (ה), vav (ו), and he (ה). Hebrew is read from right to left.