Laser
Definition
Light Amplification by Stimulated Emission of Radiation — an intense, single-color, perfectly aligned beam of light.
Technical definition
A device producing coherent light via stimulated emission in a gain medium with population inversion, amplified in an optical cavity. Properties: monochromatic, coherent, collimated, high intensity. From barcode scanners to eye surgery to fusion research.
Example
A laser pointer's beam stays narrow for hundreds of meters — ordinary light from a bulb spreads and dims because it is incoherent.
Common confusion
Laser light is not inherently more ‘powerful’ per photon — a red laser photon has the same energy as any red photon. The power is in coherence and concentration: all photons marching in lockstep.