There are some good long answers already, so I'm going to try to give as short an answer as possible.
A quantization of X$X$ is some X_hbar$X_\hbar$ depending on a parameter hbar $\hbar$ (occasionally q=e^hbar$q=e^\hbar$ instead) such that X=X_0$X=X_0$ and X_hbar$X_\hbar$ is generically "less commutative" than X$X$. This is by analogy with quantum physics where X_0$X_0$ is classical physics and hbar$\hbar$ measures the failure of position and momentum to commute.