The word “laser” is actually an acronym: Light Amplificatoin by Stimulated Emission of Radiation. What this means is that a laser is a very intense beam of light in which all the electromagnetic waves are travelling in the same direction. These waves all have the same wavelength and energy level, so the laser beam is a pure colour. This is unlike other sources of light, which produce different wavelengths of varying directions.
Lasers have several uses. Perhaps the most spectacular use of lasers is like the one below. The band Pink Floyd is famous for their light shows.