The Gods and the terminology surrounding them (Dem-ee-urg and Uhr-darn-ee)

The term 'god' can be used to represent a wide host of individuals throughout the Omniasphere. Exactly what beings are considered gods can vary depending on the religious and personal views of the person asked, but also what is meant by god can vary due to colloquial differences in language.
Generally speaking any being which is immortal is considered a deity of some sort, and often the term deity and god are interchangeable so understandably this can cause confusion. It should also be pointed out that immortal and ammortal*, could easily be perceived as the same thing by the average mortal.
Academically speaking the term 'god' is generally avoided because of it's muddled meaning, but when it is used it encompasses all such immortal beings, which may also be referred to as 'deities'. Within this broader wording they are usually split into 2 groups;

• The Demiurge / The Creator gods / The Children of Manaia- The creator gods which came before the Omniasphere
• The Uhrdahni / The Children of the Demiurge / Great old ones / Demigods - Abstract beings born from universal firmaments and forces that created the Omniasphere, or the forces introduced since by things like consciousness.
• There is also The Primurge, but this term refers to the creator of the gods and is only ever applied to Manaia - The First Mother 

Very Broadly speaking it is believed that Manaia 'birthed' the Demiurge, who in turn created the Uhrdani. What exactly the Uhrdani are is a regularly debated topic. Some believe they are the literal children of the Demiurge, others believe they are the fundamental building blocks of the Omniasphere given consciousness, some believe they are entirely accidental; like an unintentional product of creation. Thusly they can be viewed with divine reverence as children of or extensions of the gods, or as some sort of mistake worthy only of mistrust or disdain.
These terms are not necessarily accepted by religions; though most Manaians use one or other of them. However they are useful in religous studies to understand how certain faiths view different deities.

Immortality and Ammortality
*Ammortal beings are creatures that are not ravaged by the passage of time, and in some cases may be immune to other or all form of natural death. However they are not comprehensively deathless. Fiends and Celestials are commonly recognised examples, on destruction of their physical forms their souls are normally cast back to their own planes, this does not mean they cannot be killed though. It may be a difficult prospect as specific circumstances might need to be met, rituals carried out, or special weapons or spells utilised to forever stop them but they can most certainly be killed.
Immortal beings on the other hand are, at least in theory, truly deathless. It may be possible to bind or defeat their physical and even spiritual forms, but they are so deeply tied to the existence of the Omnisphere that they will always exist one way or another.
It is widely believed that the death of a creator god (or 'Demiurge') would cause whatever part of creation they made to unravel and end everything. In fact this has been written of in so many stories that literary references have coined the now-common term 'The Snarl' to represent such an event.
Where as the death of an Uhrdani might not be so catastrophic as that of a Demiurge, they are so closely tied to fundamental and constant axis' of existence like time, life, death, magic, air, etc that their destruction would be temporary at best; unless you were to somehow strip away and destroy the very concepts and dimensions of space they represent.