Cultures have developed different concepts about God or gods. This brief article gives an overview of some of the better known concepts.
The Single Instance
There can only be one. It is hierarchically the highest ever. Untouchable, unimaginable, omnipotent and omniscient. This is the core belief of the common monotheistic religions including Judaism, Christianity and Islam.
Christianity is a monotheistic religion which believes in the one creator God.
Other conceptualizations of reality prefer to deny the existence of one creator God, multiple gods, and even of other realms or dimensions at all, either because they simply do not exist or because they are irrelevant to the human being living on Earth.
This one might be a bit tricky for us Westerners...: Science as we accept it today historically is a result of the monotheistic concept of God as the only one. This concept can be traced back to Plato's search for the ultimate truth and The One founded in Greek philosophy. Coming from this end it is perfectly plausible to define Science as a (pretty young) monotheistic religion. The omniscience subject of worship is the One Truth which can supposedly be discovered by scientific methods.
Quantum Physics, Space, Time and Dimension
Science is constantly producing refutations of it's own belief in a singular truth. Quantum Physics is just one area of research that is constantly balancing on the edge of acceptance, similar to Genetics or the Evolutionary Theory. In Quantum Physics it has been proven that one thing can be different at the same time. As such it cannot be the result of One Truth. It is also pretty unclear how the universe came into existence and whether there was anything before existence began or not. Last but not least there is quite a lot of proof that there are several dimensions beyond the three plus time currently known to us. It is also perfectly unknown whether any kind of being (for example a God) populates any of these dimensions. If these beings are not constrained by space and time as we are they could probably consciously move back and forth (or rather "be" anywhere) in time and space. This would make them supernatural and omniscient, in our limited perspective godlike.
In most of the latter cases we must admit that due to lacking the sensory equipment we are unable to perceive and thus measure and reconstruct anything. Which comes close to the monotheistic concept of one omnipresent, omnisiceint and omnipotent God - just that it is not a "person" as we human beings but just some other for us completely unintelligible entitiy. Just like we exist from electrons and protons and atoms and molecules and cells and limbs which in the end are one body. No electron can have a perception of what a human being constitutes. See also Alanis Morissette as God in Dogma.
The Concept of Multiplicity
Other religions have favored a concept of multiplicity i.e. there are several or even many gods. This has been the case with the Greek who had a whole nation of gods. Extremely jealous, greedy, obsessed and biased gods at that. Not exactly role models or if so very questionable ones.
Other religions - or maybe rather 'beliefs' - postulate that we are God, that each single one of us has God in ourselves.
Gods as Beings of another Dimension
Some cultures have developed a metaphysical model which separates the world as we know it from other dimensions. Interestingly this permeates many cultures, albeit in very different ways. In the Western Christian culture there is a deep old belief in ghosts. In this context ghosts are kind of energetic and conscious remnants of the deceased. They exist in a parallel universe.
Other cultures can describe parallel dimensions more precisely. Mathematicians for example can describe 3, 4, 5 and even N-dimensional worlds.
Other cultures describe several different dimensions which are populated by specific beings differing from "our" world. There are dimensions with form and without form and with completely different time scales. Beings on those other dimensions will therefore also perceive differently to us which is why under normal circumstances we cannot see, hear or feel them. In these cultures gods, demi gods, hungry ghosts and hell beings are just other sentient beings. They have more power and suffer less or have no power and suffer incredibly or anything in between (like us human beings).