What are filter banks and what's their application? What's the meaning of $H(z)$ in descriptions of filter banks?
A filter bank is a collection of bandpass filters designed to split a signal into a number of bands. The centre frequencies of the band pass filters can be spaced linearly or according to a non-linear spacing depending on the intended application.
$H(z)$ denotes the $z$-domain transfer function of a filter in the bank.