Yahweh is the personal name of God, revealed to Moses at the burning bush. When Moses asked God's name, the answer was I AM THAT I AM — a name built on the Hebrew verb to be, declaring God as the self-existent, eternal one who simply is. From it comes the sacred four-letter name (YHWH) that the King James Version renders, in capital letters, as the LORD.
So holy was this name that ancient Jews would not pronounce it, saying Adonai (Lord) instead when they read. Every time you see LORD in small capitals in an English Bible, the Hebrew is Yahweh — God's covenant name, the name of the one who keeps his promises. When Jesus said before Abraham was, I am, his hearers took up stones, for they knew exactly which name he was claiming.
Yahweh in Scripture
And God said unto Moses, I AM THAT I AM: and he said, Thus shalt thou say unto the children of Israel, I AM hath sent me unto you.