The peak of the wave is the highest point and the trough is the lowest point. The period of the wave gives you the time it takes for the wave to move through one wavelength, or one cycle. Instead of the wave's period, you can talk about the wave's frequency , which tells you the number of cycles of the wave per second at a point. The speed of the wave tells us how fast it travels in the medium. It depends on the medium in which the wave is traveling.
Sound travels slower in air than in water.
Sound travels slower in water than in wood.