Spectral efficiency

Spectral efficiency is a measure of how much data can be transmitted in a certain amount of frequency bandwidth. We can think of frequency bandwidth like a highway: the wider the highway, the more cars it can fit. So, for more data to be transmitted, we need a wider frequency bandwidth, just like we need a wider highway for more cars to fit. This is why spectral efficiency is important - it lets us measure how many cars (or data) can fit on a certain size highway (or frequency bandwidth).