The tetragrammaton or four tetras “YHWH”, is the name of “God” in Hebrew, which had no “vowels”. God Himself gave it to us in Exo 3:14, saying “I am who I am” and “I am”. Jesus appropriates this “I am” 7 times, in John 6:35, John 8:12, John 8:58, John 10:7, John 11:25, John 14:6, John 15:1.
When pronouncing it in our languages, you have to put vowels on it, and they usually put the “a” and the “e”, leaving “Yahweh”, or “Yahveh” or “Yavé”. Or more changes are made, leaving “Jehovah” or “Jehovah”, by changing the “Y” to “J”. See “God.”
Christian Bible Dictionary
Dr. J. Dominguez
http://bible.com/dictionary/
Source: Christian Bible Dictionary