YHWH is a transliteration from Hebrew into English of God’s personal name. It is sometimes called the tetragrammeton, which comes from Greek and means “four letters.”
Y stands for yod — י
H stands for hey — ה
W stands for waw or vav — ו
H stands for hey — ה
It looks like this in Hebrew, but remember that Hebrew is read right to left.
In English translation, it is usually transliterated by Jehovah or Yahweh. Transliteration is the giving of the letters of one language in the letters of another. One of the problems of transliterating YHWH is the question of what vowels go with these letters. Hebrew is written without vowels except when dealing with the Masoretic text. The Masoretes were Jewish scribes from about A.D. 500 to 1000, who provided vowel points (vowel indicators) to aid with correct pronunciation. However, YHWH was not pronounced out of reverence for God, and the correct pronunciation can only be guessed at now. When a reader reached this point in the text they would say either adonai (my Lord) or elohim (God) — the latter being said when YHWH appeared with the word “lord” already. The Masoretes put the vowels for adonai or elohim on YHWH in the text since the reader was actually going to say adonai or elohim.
Jehovah as a transliteration goes back to ecclesiastical Latin in the 16th century A.D. or possibly even as far back as 1100 A.D. However, the transliteration was made with the vowels of adonai (my Lord). Yahweh is the attempt of modern scholarship to determine the correct vowels for YHWH and indicate that in the transliteration.
YHWH occurs over 6000 times in the Old Testament. The King James Version only renders 4 of those occurrences as Jehovah. The ASV is more consistent and has Jehovah 6779 times. Other translations use LORD or GOD in all capital letters to indicate YHWH following the later Jewish practice of saying either adonai (my Lord) or elohim (God) when encountering the divine name.
As a Bible reader, I like to know this background so that I’m aware of God’s personal name and be able to identify when it occurs, because certain passages make more sense that way.
So he built an altar there and called upon the name of the LORD and pitched his tent there… (Genesis 26:25, ESV) — Lord is a title. YHWH, however, is a name. When you understand that LORD is standing for YHWH, the passage makes more sense.
But Pharaoh said, “Who is the LORD, that I should obey his voice and let Israel go? I do not know the LORD, and moreover, I will not let Israel go.” (Exodus 5:2, ESV) — Pharaoh is saying he doesn’t know YHWH as opposed to the gods of Egypt whose names he did know.
I am the LORD your God, who brought you out of the land of Egypt, out of the house of slavery. (Exodus 20:2, ESV) The preface to the Ten Commandments names YHWH as the one who has delivered them. They lived in a polytheistic setting. This identification is important.
The above passages are examples. In many places, knowing that you are dealing with the divine name helps make the passage clearer. The preface to most modern Bible translations are going to tell you how the translators have chosen to handle the divine name.