The “g” stands for generation. So it’s the 5th iteration of the technology versus the 2nd iteration. Whilst there are many improvements (speed, capacity, security etc) there are some negatives. (I believe mainly to do with signal penetration - i.e. getting a signal in basements, stone wall houses, being behind objects etc.)

Where I’m currently staying I have: 2G, edge, 4G and 5G signals available.