The laser is a device that a beam of light that is both scientifically and practically of great use because it is coherent light.
Light is just like radio waves in the way that it can also carry information.
The information is encoded in the beam as variations in the frequency or shape of the light wave. The good part is that since light waves have much higher frequencies they can also hold much more information. Not only is the particle the smallest light unit but it is a particle as well as a wave. Even if the light is of a single frequency that statement would also be true. A laser is useful because it produces light that is not only of essentially a single frequency but also coherent, with the light waves all moving along in unison.