What is 3G explained?

3G is the third generation of wireless mobile telecommunications technology . … This ensures it can be applied to wireless voice calls, mobile Internet access, fixed wireless Internet access, video calls and mobile TV technologies.

There are a number of use cases and applications for 3G technologies:

If you see a 3G at the top left it means that you are in an area that does not have 4G support . When you are in an area with 4G (or, on Verizon, LTE) you will see that in the top-left corner instead.