Omnipresence is described (though not fully defined) in Psalm 139: 7-12 as God being everywhere in spirit.
Where can I go from Your Spirit?
Or where can I flee from Your presence?
If I ascend to heaven, You are there;
If I make my bed in Sheol, behold, You are there.
If I take the wings of the dawn,
If I dwell in the remotest part of the sea,
Even there Your hand will lead me,
And Your right hand will lay hold of me.
If I say, “Surely the darkness will overwhelm me,
And the light around me will be night,”
Even the darkness is not dark to You,
And the night is as bright as the day.
Darkness and light are alike to You
God is omnipresent in all reality, in the most remote areas & in the darkest places, even in Sheol.
I used to think Hell was the only place that lacks God’s presence because sinners will not be restrained by God’s grace or blessed there, but since God’s judgement is just he must be directing its operations as well