Standing Wave Explanation by Superposition
Superposition is the term for one thing being laid over top of another. If a standing wave and reflected wave are combined, or superimposed, then the sum can be a standing wave.
Press start to see the standing wave created when you oscillate the end of a long spring which is held at the other end.
Click http://www.walter-fendt.de/ph14e/stwaverefl.htm link to open resource.