Time Remnant

When someone goes back in time, they change the course of history. Meaning their timeline no longer exists from them altering it. This causes them to become a remnant of this old timeline whom is now living in the new altered timeline.

Example: You go back in time and kill your ancestor. You no longer exist, meaning you are now a remnant of the timeline where your ancestor lived and you existed.

Martin Stein: "The reason we cant find any evidence of his existence is because he isn't supposed to exist. He is a time remnant"