What does "coherent" mean when describing laser light?

When describing laser light, "coherent" refers to the property of the light waves having a constant phase relationship with each other. This means that the waves are organized, with a constant difference in phase, allowing them to travel in unison rather than at random. Coherence is fundamental to the nature of laser light, as it enables the formation of a tightly focused beam that can be intensely powerful and highly directional.

This organized nature of the light waves is what allows lasers to produce such distinctive characteristics, such as high intensity and the ability to maintain a narrow beam over long distances. In contrast, light sources that are not coherent, like traditional incandescent bulbs, emit waves that are randomly phased and dispersed in various directions, leading to a diffused light rather than a concentrated, focused beam.