Laser stands for Light Amplification by Stimulated Emission of Radiation.
A green laser is a device that projects a highly concentrated narrow beam of light which is amplified to great brightness using stimulated radiation.

What are lasers used for?

Lasers are used for a variety of purposes including pointing out objects during a presentation, aligning materials at construction sites and in the home, and by doctors for cosmetic and surgical procedures. Many items you encounter on a daily basis use lasers, including CD and DVD players; bar code scanners; dental drills; laser-guided tools, such as levels; and blue laser pointer

What is wavelength?

Our eyes are sensitive to light which lies in a very small region of the electromagnetic spectrum labeled "visible light". This visible light corresponds to a wavelength range of 400 - 700 nanometers (nm) and a color range of violet through red. The human eye is not capable of "seeing" radiation with wavelengths outside the visible spectrum. The visible colors from shortest to longest wavelength are: violet, blue, green, yellow, orange, and red. Ultraviolet radiation has a shorter wavelength than the visible violet light. Infrared radiation has a longer wavelength than visible red laser pointer light. The white light is a mixture of the colors of the visible spectrum. Black is a total absence of light.

How does wavelength affect laser visibility?

In non-technical terms, the closer the wavelength is to 555nm, the brighter it will appear relative to other colors of the same high power laser pointer. The brightest color is green, followed by red, then blue, then violet.

What do you mean by laser “radiation”? Does it go through the body or cause cancer?

Some lasers emit radiation in the form of light. Others emit radiation that is invisible to the eye, such as ultraviolet or infrared radiation. In general, laser radiation is not in itself harmful, and behaves much like ordinary light in its interaction with the body. Laser radiation should not be confused with radio waves, microwaves, or the ionizing x-rays or radiation from radioactive substances such as radium.

Does laser radiation make things radioactive?

The use of the term radiation has occasionally led to a misconception that lasers make things radioactive. Normal applications do not have powerful enough beams to exceed the energy threshold for this. Only a few large Rechargeable Laser Pointer have the ability to potentially make target materials slightly radioactive. The term radiation is used because the beam radiates out from the laser.