Bandwidth And Data Transfer

i came across this

Simply put, bandwidth refers to how much data can be transferred at a time. Data transfer relates to how much data is actually being transferred. Think of it this way: If bandwidth were a bridge, then the bigger the bridge, the more vehicles can pass over it. Data transfer, on the other hand, can be compared to the number of vehicles allowed on the bridge in a given period of time.

and i access to my web host manager
i see there view bandwidth usage link

so it shows usage in percentages....(increases as month passes...)

so if we go by defination, is it really bandwidth they are showing or is it data transfer they are showing to us...?

(bandwidth refers to how much data can be transferred at a time,so it is fixed ...means if 3gb is given ....then it cannot be said 80% of 3gb used.....here 3gb should mean any data higher than 3gb cannot pass ...though this site at an instance ...isn't that...)

And why is data transfer not so used term in webhosting if it that important ...means i have not seen many people saying 500gb datatransfer rather than saying 500gb bandwidth...(as it seems completely different from defination...)

From defination,data transfer seems to be more important than bandwidth...