First, some background on YHWH:

The Old Testament was written in Hebrew and Hebrew was not written with vowels. In the original Hebrew, God’s name is YHWH, known as the tetragrammaton. The Jews quit pronouncing the name of God because of the fear of accidentally taking His name in vain (Leviticus 24:16). Rather, they substituted the word Adonai (Adhonay) meaning Lord.

Because of the lack of vowels, Bible scholars debate how the tetragrammaton YHWH was pronounced. [Jehovah was developed by Christians probably in the 16th century, inserting the vowels of adonai (Hebrew for Lord) or elohim (Hebrew for God, a plural word) into the tetragrammaton.]

YHWH refers to God’s self-existence. He described Himself in Exodus 3:14 to Moses as “I AM WHO I AM.” The essential meaning of the tetragrammaton is self-existent.

Greatly condensed from: GotQuestions.org

Some quotes about the use of Jehovah:

Jehovah: “Intended as a transliteration of Hebrew YAHWEH, the vowel points of Hebrew ADHONAY (my lord) being erroneously substituted for those of YAHWEH; from the fact that in some Hebrew manuscripts the vowel points of ADHONAY (used as a euphemism for YAHWEH) were written under the consonants YHWH or YAHWEH to indicate that ADHONAY was to be substituted in oral reading for YAHWEH. Jehovah is a Christian transliteration of the tetragrammaton long assumed by many Christinas to be the authentic reproduction of the Hebrew sacred name for God but now recognized to be a late hybrid form never used by the Jews.” (Webster’s Third New International Dictionary)

Jehovah: “False reading of Hebrew YAHWEH.” (Webster’s Collegiate Dictionary)

Jehovah “is an erroneous form of the name of the God of Israel.” (Encyclopedia Americana)

Jehovah: “the pronunciation ‘Jehovah’ is an error resulting among Christians from combining the consonants of YHWH with the vowels of ADHONAY.” (Encyclopedia Britannica)

Jehovah: “false form of the divine name YAHWEH.” (New Catholic Encyclopedia)

Jehovah “is a mispronunciation of the Hebrew YHWH the name of God. This pronunciation is grammatically impossible. The form ‘Jehovah’ is a philological impossibility.” (The Jewish Encyclopedia, p. 160)

Jehovah: “an erroneous pronunciation of the Tetragrammaton, or four-lettered name of God made up of the Hebrew letters Yod He Vav He. The word ‘Jehovah’ therefore, is a misreading for which there is no warrant and which makes no sense in Hebrew.” (The Universal Jewish Encyclopedia)

Jehovah “is an erroneous form of the divine name of the covenant God of Israel.” (The New Schaff-Herzog Encylopedia)

Jehovah “is an artificial form” (The Interpreters Dictionary of the Bible)

Jehovah: “the vowels of one word with the consonants of the other were misread as ‘Jehovah.'” (English Encyclopedia International)

Jehovah “is an inaccurate reconstruction of the name of God in the Old Testament.” (Merits Student Encyclopedia)

YHWH: “When Christian scholars of Europe first began to study Hebrew, they did not understand what this really meant, and they introduced the hybrid name ‘Jehovah’…THE TRUE PRONUNCIATION OF THE NAME YHWH WAS NEVER LOST. Several early Greek writers of the Christian church testify that the name was pronounced ‘YAHWEH.’ This is confirmed, at least for the vowel of the first syllable of the name, by the shorter form Yah, which is sometimes used in poetry (e.g., Exodus 15:2) …T he personal name of God of Israel is written in the Hebrew Bible with the four consonants YHWH and is referred to as the ‘Tetragrammaton.’ At least until the destruction of the First Temple in 586 B.C.E. this name was regularly pronounced with its proper vowels, as is clear from Lachish Letters, written shorty before that date.” [Encyclopaedia Judaica (Jerusalem), Vol. 7, p. 680]

Jehovah God: “a supreme deity recognized and the only deity worshiped by Jehovah’s Witnesses.” (Webster’s Third New International Dictionary)