What is the difference between radiation and radioactivity?

All matter is composed of atoms.
When an atomic nucleus, the center of an atom, divides and turns to some other substance, it emits radiation.
Radioactivity is the ability to emit radiation and turning into another substance.
Uranium and other substances that naturally emit radiation and turn into other substances are called radioactive materials.
The figure below uses the metaphor of fireworks to explain radiation.

In nature, the atomic nuclei of various substances divide and emit radiation, but the level is too low to affect the human body.