Some hearing aids have multiple channels. That is, they have frequency ranges that are processed completely independently from each other. They have two or more independent amplifier paths.

This allows them to better tailor their response to the differing needs a patient might have over various frequency ranges.

Some hearing aids accomplish similar differientiation using bands, which allow differing filtering over different frequency ranges.

People frequently use the term "band" and "channel" interchangeably, but they are slightly different.