Time remnant

"It's possible Eobard was in the Speed Force, protecting him like a bomb shelter, keeping him alive and his timeline intact. It's what's known as a 'timeline remnant'."

- Harry Wells on Eobard Thawne

Time remnants, or timeline remnants, as dubbed by Harry Wells, are a phenomenon that occurs as the result of meta-human speedsters' time travel abilities. Due to possible time ruptures and changes brought by the speedsters traveling (and/or staying) further back in time or even a speedster's death, the time remnants are preserved via the Speed Force as if in their original timelines, have to appear in the new timeline in order to prevent further time paradoxes.