Although we encounter it frequently, the term quantization seems to be quite unfamiliar. For example, money is quantized. The Banknotes are integral multiples of the coins. As you have learnt in grade 11 in the topic of waves, a stretched string oscillates only in definite stationary states whose frequencies are quantized. In Bohr model of an atom, electrons orbit a nucleus at a specific distance from the nucleus. The electron orbits are direct result of the quantization of energy. Hence, the bright lines of different colors at sharply defined wavelengths in the emission spectrum of hot objects we have mentioned above corresponds to a package of energy or quanta of energy called photons. An electron can radiate or absorb energy as radiation in quantized amounts.