First of all, quantization is the process describing the transition from a classical theory to the corresponding quantum theory. For instance, if you quantize classical electrodynamics, you will end up with its quantum version, quantum electrodynamics.

On the other hand, to be quantized means for a physical quantity to be divided into little building blocks or packets. For instance, in quantum theory, the energy of light is quantized: a given quantity of light consists of a finite number of energy packets called photons.