How many frequency channels are there in a frequency band?

I've often heard people saying that 4G uses the 1800 MHz band but precisely what all frequencies does it work upon? Does it mean that is just uses one frequency i.e. 1800 MHz, well in that case wouldn't there be interference among signals carrying different data.

1. What is the difference between a frequency band and frequency channel?
2. Why don't we directly use frequency ranges to tell what a particular technology operates upon instead of telling what band it uses. For example, why do we say that 4G uses 1800 MHz band instead of saying it uses frequencies between X MHz and Y MHz. Wouldn't it be easier to understand?