Lord GOD
is a translation of the Hebrew word Adonai
and the divine name Yahweh.
The divine name, commonly referred to as the Tetragrammaton, is normally translated as Lord.
Adonai
is normally translated as Lord.
When these two names stand together, the NIV has chosen to translate them as Sovereign Lord
and the ESV as Lord GOD.
A more literal translation would be My master the Lord.
1
1 This is what the Lord GOD showed me: behold, a basket of summer fruit.