Light
Light waves are transverse waves of an unusual sort: they don't travel through a previously existing medium, but generate their own medium to travel through. (See EM Waves for details.) Thus light is the only type of wave which can travel through vacuum. Light in vacuum travels faster than any other known object or wave, with a speed of $3\times 10^8\u{m/s}$; this is known as $c$. In other materials such as glass or water it travels more slowly, as we'll discuss in [Missing Link].We experience the amplitude of light as its brightness, and the frequency of light as its color. However, humans can see only a very small portion of all light waves, or what is called the electromagnetic spectrum.
Like sound, most "colors" we see are actually a combination of different frequencies. (Notice that the rainbow doesn't include pink, for instance, or brown, or grey.) In fact, our eyes are actually rather bad at distinguishing between different combinations of frequencies. For example, the yellow you see in an actual rainbow is a single pure frequency of light. However, since computer screens are only able to show us various combinations of red, green, and blue, the yellow in the diagram above is an entirely different "color", a mixture of red and green. The fact that we see them as the same color is due to the "deficiencies" in our eyes.