Two lines that lie on top of one another are called coincident lines.
Coincident Lines
See also
Coincident, Intersecting Lines, Parallel Lines, Skew LinesExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Coincident Lines." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/CoincidentLines.html