I'm interested in a word (noun) to use to refer to an object or concept which has permanence.
For example, substituting ###, I would say
"Many of the objects we interact with in real life are ###s, if you leave a ### for a while it will still exist when you come back. But some things, like an ice cube, a bad smell, a virtual particle in physics or a local variable in programming, are not ###s."
The antonym, a word for an item which displays impermanence, would be interesting as well.
The motivation is that I want to name an abstraction in my computer program. It is a type of container to put data in, instances of this container will hold data that (has) more permanence than a typical data (element) will. Typically, you name an abstraction after the thing it represents. If you have an abstraction that holds data about one person, you name the abstraction itself "Person". While trying to name this abstraction, I got curious to know if there was a generic word.