Everlasting Cat

The Everlasting Cat is mentioned in the hymn section of "Jellicle Songs for Jellicle Cats":

 The mystical divinity of unashamed felinity Round the cathedral rang "Vivat!" Life to the everlasting cat! Feline, fearless, faithful and true To others who do what

The same section is sung by the ensemble again in "The Journey to the Heaviside Layer", as the cats watch Grizabella ascend to the Heaviside Layer.

A common fandom interpretation is that the Everlasting Cat is a god-like figure who is revered by the Jellicle Cats and has a connection to the Heaviside Layer. Another interpretation is that the cats are referring to their species in general, and not one particular figure.

The term has wormed its way into Cats fanspeak, with the fandom often using it as a replacement for "god" and other similar expressions (e.g. "Everlasting Cat!" instead of "Good Lord!").