First I would draw a graph showing a wave to support my explanation for what the wavelength means. The wavelength of a wave is the distance, in metres, from one point of the wave to the same point on the next wave. One easy way of doing this is to measure from the peak of one wave to the peak of the next wave. To further explain this, I would annotate the wavelength on the graph as well as the peak of the wave. I would also show that the wavelength constitutes a whole wave cycle by highlighting this on the graph.