Answer:
Something which is short-lived or passing is called ephemeral.
Explanation:
The word ephemeral means that something lasts for a really short period of time. It is a word widely used in literature since this can characterize someone or something that will be a brief time in the story, it is a very abstract term since the word that is related to it, time is an abstract noun itself, the concept of time varies according to different perspectives.
