Light, more appropriately visible light, is just a small portion of the energy spectrum, which ranges from radio waves with very long wavelengths to x-rays to cosmic rays (very short). A wavelength is the distance between the two tops (or bottoms) of a wave. The light we see has different wavelengths. Red is the longest, with a wavelength of about 700 nanometers (nm); blue is the shortest, at about 400 nm. Some include the regions just outside our vision as visible light; infrared and ultraviolet.
Our eyes see all of the visible spectrum as one color, white. A prism or other refracting body can separate colors since each color will bend slightly differently. That is what a rainbow is; white light bouncing through - and being separated by, water droplets.