Omnipresence
Omnipresence means being everywhere all at once. It may include being not only in in all of space, but in all of time. The most meaningful kind of omnipresence includes being present in all of space and at all times.
There are only two kinds of things that can be omnipresent, but each in a different way: everything other than God, and God Himself alone.
God is everywhere within His Creation, but God also transcends, or is beyond, His Creation.
Building the concept of Omnipresence one logical bit at a time
The belief of Pantheism (that the Creation is God) may be the result of admitting the natural sense that God is omnipresent while rejecting, or else failing take into account, the sense that God is transcendent.
In contrast to Pantheism is Deism. Deism may be the result of believing in the transcendence of God while failing to see how God can be present in His Creation.
In any case, there is a dualistic view of God's omnipresence and God's transcendence. This is the view that God's omnipresence is different from God's transcendence. So, there is a need to accept both God's omnipresence and God's transcendence.
So, on the face of it, there seems to be a problem of balancing God's omnipresence with God's transcendence. There seems to be an effort needed to keep from being forced to one side or the other. Deism or Pantheism. Is God more transcendent that He is omnipresent? But, we assume that His transcendence and omnipresence are equally 'weighted', then, by what logical mechanisms can we see them as such?
But, there may be at least one way to resolve the seeming conflict between God's omnipresence and God's transcendence: by allowing that the classical geometric point may actually exist.
The classical geometric point is any point in space which cannot be divided into smaller spaces. This means that this point, if it exists, actually has no space. It's simply there, everywhere, in all of space, and in all of matter. It takes up all of space without taking up any of it.
From a classical view of physics, such a point allows that all of space and matter is infinitely divisible. In any case, if there really does exist a true, space-less point, then that point can be thought of as a kind of 'doorway' between God and all of His Creation. God can, then, be transcendent in the same way that He is omnipresent. In other words, He doesn't need to have extended Himself in order to be omnipresent. He doesn't need to take your chair from you in order to be in your chair: He can be in your chair right along with you without forcing you to one side.