Immuteble describes data, whereas an API call is more like a function call, in which case we'd call the property "referential transparency", which means, a func

Immuteble describes data, whereas an API call is more like a function call, in which case we'd call the property "referential transparency", which means, a function always returns the same result for a given input value. "referential transparency" makes up half the definition of a "pure" function, with the other half being the absence of side effects.