The phrase "unseen entity" refers to something or someone that cannot be seen or observed. It implies the presence of an unknown or invisible entity that cannot be visually detected. Full definition
It was the expression of living realities in the world of nature, as well as a reminiscence of epochal events in the nation's history, which were by various lines of thought accepted as symbols and figures of unseen entities of human life. (religion-online.org)
In the game, Luigi inherited a spooky mansion lurked with unseen entities provided he can muster the courage to spend a night within its confines. (superluigibros.com)
The particle is the calling card of an unseen entity called the Higgs field, which is thought to give all particles their mass. (newscientist.com)