Laser is a word formed from the acronym "Light Amplification by Stimulated Emission of Radiation."
Light from a laser is both temporally coherent, meaning it is of a single pure color, and spatially coherent, meaning that it can be easily formed into a thin beam or focused to a small spot. The angle at which a laser beam spreads is determined by diffraction; a wide beam will diverge more slowly than a narrow beam. Many cheap laser pointers exhibit excess beam dissipation due to cheap manufacturing, and shoddy construction.
The use of lasers is very important in science and medicine; they have also become ubiquitous in CD-ROM and DVD players and as pointers.  They're also used in bar code scanners. In recent years, lasers have even become a seemingly effective weapon for certain militaries. They seem effective against a variety of targets, including planes, missiles, and ground vehicles.
The world's biggest and most energetic laser is the National Ignition Facility (NIF) located at Lawrence Livermore National Laboratory (LLNL) in Livermore California.