Those who write in the fantastic mode (which is one thing I aspire to do) often are faced with the need to invent one or more gods or other powerful spirits to sit at the helm of the worlds they set their works of fiction in. How do we come up with interesting and meaningful gods for these worlds, and breathe life into them, and the divine/celestial systems they rule over? It requires an understanding of different ways the notion of gods can be interpreted, which are not mutally exclusive, but stand side by side one another like tools in a tool box
Below you will find five ways I came up with very quickly (hence casually) in the course of my working through this topic.
This sense is perhaps the simplest. Any being that is very powerful, relative to another species of being, may be interpreted as a deity by merit of that alone. According to this understanding, if a species of alien that was technologically superior to humans came to the earth and subjugated them, even if that subjugation were purely of a politcal (and not a spiritual, etc.) nature, they could still be rendered in the language of fantasy as deities.
Another understanding is founded on the feeling of reverence human beings feel towards the beings or powers that gave rise to them and their society. This is the impetus behind the practice of ancestor worship found across the ancient and modern world. In this sense, anything that is perceived and revered as a source, is seen by those who have arisen from this source, as a god, and who likewise may be seen as such themselves by their descendents, of whom they are the (less remote) source, in additionp to the more aboriginal (more remote) source.
Because the act of origination is highly specific as to its object, this sense of gods tends to inspire a unique resonance between the god and the lesser beings that see him as such. That is why gods in this sense often are of an ethnic nature, or belong to a culturally-specific pantheon, may even be seen as gods exlusively of the particular race of people in question.
An inspection of any mythology from anywhere in the world will reveal, not simply a roster of the names of abstracly powerful beings, but will usually clarify to some extent what the nature of their power is, which creates a real exponent of that gods power and so makes it observable in the natural world. Often this is a force of Nature or some other abstract Idea which is believed to be somehow essential and intrinsic to the World and requisite for its proper functioning.
An exmaple of the former is the Wind, or Rain, or Lightning; while examples of the latter include Love, Future, Revenge, and so on. Some things which may not seem at first glance to constitute Ideas that are essential to the world (an ugly emotion like Revenge, for example), it must be noted, are in a manner of speaking elevated to such a status when they are given as the domain to a god; but this is an interpretative choice made by the mythopoet
Here "existential" means related to the World (I partially have in mind Heideggar's concept of World), so while these beings may seem to resemble #3, they differ in that they are abstracted by an extra level, to be stand-ins for the World in question itself, or for certain abstract qualities that inhere in it. A "creator deity" belongs to this type. The World "stands for" such a Being, as his creation; he may be identical to it (immanentism, pantheism), or be separate from it, and non-identical (transcendentalism, deism).
This is a postulate that may be inferred from the commonly-observed tendency of religions to undergo cyncretization, whereby for instance Greek gods are identified as Roman ones and vice cersa, or how the Shinto deities are seen as manifestations of more abstract and excellent Buddhist ones. And this too is a phenomenon that is happily translated into the language of fantasy. So that, when the text refers to one deity by one name, the one who is named such can be called also by a different name at a different time or in a different context. To take one possibility out of many, by a different character, who hails from a different homeland, or who is the disciple of a different religio-philosophical sect. But this means that any text that does make use of this device has to situate itself at a certain standpoint within (or without, to introduce a touch of irony) the World it has created, where the context will justify the use of this name or another, in various contexts.