Mobile network generations and bandwidth

I have couple of question related to mobile network generations:

1) While comparing generation of mobile network people mention that 1G and 2G has to use maximum bandwidth. What is bandwidth in this content and why they use maximum bandwidth?
2) 1G and 2G are narrow band networks. What is narrow band here?
3) 3G and 4G are wide band networks. Don't they use maximum bandwidth?

Thanks and Regards,
Deepa

---