Levels

'Levels' are a colloquial name for the various iterations of reality, in other words parallel dimensions, that exist across the multiverse. Levels can be accessed via the Labyrinth. Levels do in many cases have a similarity and individuals can and do exist across multiple levels at once, living lives that may be similar or varying amounts of difference from one to another. For instance, Jim Thurmond and his family, including his son Danny and wife/ex-wife Tammy, exist both in the 'Rising Universe' as well as the 'Clickers vs Zombies' universe, and it is remarked upon by Ob that he has killed Jim or been killed by him multiple times. Levels are able to be accessed through the Labyrinth, and perhaps through other 'brute force' methods as seen with the attempted summoning of Nodens, or the multiple invasions by the Siqquism which destroyed at least four instances of Earth.

Quote
“That’s what they call all the different worlds. All the different realities. They’re levels. Each level can be reached by going through the Labyrinth.” - Dez, the Darkness at the Edge of Town

“We’ve met before, on other worlds than this. You blew me up once, in the sewers beneath New York City. And you dropped me off a mountain in West Virginia. And out of an airplane, once. Oh, and you cut my head off in Japan. Those are the times I remember, at least. I’m sure there were more. When you are as old as me, you sometimes forget the little details. But I certainly haven’t forgotten you, Jim Thurmond, or your brat there, or your friends Frankie and Martin.” - Ob, Clickers vs Zombies