Question

what is radiation

Answer 1

radiation means to radiate, to travel through a medium or in vacuo.

if you're referring to electromagnetic radiation, that refers to "light" whether it's visible, heat (infrared), radiowaves, x-rays, etc.

Answer 2

Radiation is energy that comes from a source and travels through space and may be able to penetrate various materials. Light, radio, and microwaves are types of radiation that are called nonionizing. The kind of radiation discussed in this document is called ionizing radiation because it can produce charged particles (ions) in matter.
http://hps.org/publicinformation/ate/faqs/whatisradiation.html

Answer 3

when you quote something, you should use quotation marks (" ") to avoid plagiarism.

Answer 4

that's why i sourced it. But in the Future i will use your advice. and put some Quotation marks. @aaronq