A laser beam can be best described as:

A laser beam is fundamentally produced through a process involving stimulated emission in a medium that is typically contained within an optical resonator. When the light within this resonator interacts with the excited atoms or molecules, it can stimulate them to emit additional photons, which leads to the amplification of light. The nature of lasers is that they produce coherent, monochromatic, and directional light.

Choice B accurately reflects this concept, as it refers to the light that escapes from the optical resonator after being amplified. It highlights the characteristic nature of lasers, distinguishing them from ordinary light sources.

Other descriptions may imply general properties of light rather than specifically capturing the essence of a laser. For example, characterizing a laser beam as a concentrated high-energy beam does not convey the specific processes involved in its generation. Similarly, stating that it is regular light amplified by a lens does not account for the crucial role of the optical resonator and the coherence of the emitted light. The description of a standard visible light beam is too broad and lacks the distinct attributes that define a laser beam.