Omnipresent describes something that's everywhere at once, like a deity or a bad smell.
You might recognize the prefix omni-, meaning "all," from words like omnipotence (all powerful), or omniscient (all knowing). Add it to -present, and voilà, there's something that's present all the time, like Santa Claus who sees you when you're sleeping and knows when you're awake. You can't hide from an omnipresent being. Hair splitters prefer that a bad smell be ubiquitous (turns up everywhere) and save omnipresent for the divine. And Santa.
