Elision is the leaving-out of a sound — the name of what happens when we elide. Every language does it in fast, natural speech; English just does not always write it down. You hear elision when every sounds like evry, or when next time runs together. In poetry, elision is a tool for rhythm. Teachers of French talk about elision a lot (l’ami), but English has it too; we are just less tidy about marking it. It is a school-and-linguistics noun. In careful writing, some people also use elision for leaving a fact or a distinction out of a story, but the core meaning is still the missing sound.