Bullying someone or otherwise acting cruelly is victimization. If you deliberately take advantage of your little brother's small size and good nature by eating his cookies as well as your own, that's a kind of victimization.
You can use this word for the action of victimizing someone (essentially singling them out and making them your victim) or the process of being victimized. Your victimization at the hands of that horrible substitute gym teacher was truly unfair, especially when he made you do 50 pushups while the rest of the class played volleyball. Victimization is often a very serious matter, since it is a result of an imbalance of power, lack of justice, and cruelty.