"Eternal separation" refers to being permanently apart or disconnected from someone or something for an infinite amount of time. It conveys the idea of never being able to reunite or be together again, forever apart. Full definition
The death penalty for sin is not only the death of the body but eternal separation from the creator. (religion.blogs.cnn.com)
And another thing, you said that the only description we have is the one of eternal separation. (religion.blogs.cnn.com)
By even 1 mortal sin — a fully - knowing and fully - deliberate act against God's law (the 10 commandments)-- you reject God, too, and thereby merit eternal separation from God and punishment in Hell. (religion.blogs.cnn.com)