What is radioactivity ? Explain with type and example?

Radioactivity defined as the spontaneous emission of particles (alpha, beta, neutron) or radiation (gamma, K capture), or both at the same time, from the decay of certain nuclides that these particles are, due to an adjustment of their internal structure.

Radioactivity can be natural or artificial. In natural radioactivity, the substance already has radioactivity in the natural state. In artificial radioactivity, the radioactivity has been induced by irradiation.
~ nuclear-energy.net/definitions/radioactivity.html

"Radio" is a Latin word meaning "I throw", specifically meaning to throw seeds by hand. In English that is called "broadcast". Radioactivity means a nucleus expels a particle of some sort, throwing it in random directions.