Answer:
The root word behind radiation is radius. In radiation, the effect travels out from the source in all directions unless otherwise constrained.
EM radiaton is the radiation of an EM wave from some source. Examples are radio, light, x-rays and so on.
Radioactive radiation is the emission of an actual particle. Alpha, Beta and Gamma radiation are examples. These usually have high energies, and some may cause damage to material in the vicinity. As in Accelerator radiation used to destroy cancers.
Sound radiates from its source.
The same term radiation is also used to describe the spreading out from a point, even if it is not along radii. The radiation of a peoples or a botanic species are examples.