If we ask: What is radiation?, we first have to figure out what we mean by that. Let’s say “radiation” refers to the bad stuff that comes from radioactive substances or devices. Examples of radioactive things are: radon gas, nuclear fallout, radioactive waste, etc.
This is properly called “ionizing radiation.” But most of the time people just call it “radiation.”
It occurs via waves or particles emitted from radioactive things. The most common examples have names. Alpha particles or alpha radiation are collections of 2 protons and 2 neutrons (a.k.a. helium nuclei). Beta radiation is a stream of electrons. Gamma radiation is an emission of gamma waves.
