The amount of data that a server is able to transfer in a specific amount of time is called as bandwidth.
Unmetered hosting doesn’t mean that you can get unlimited traffic on your website. You always get limited traffic, practically but other factors: time and throughput.
When a hosting company offers unmetered bandwidth, it means that they offer a definite amount of bandwidth (for example, 1Gbps) that you can use as much as you want to. You get limited maximum server speed, but the data you can transfer is unlimited.
In a metered bandwidth, the host monitors the amount of data used by you and charges you as per the amount per month. So, the more are your site visitors, the more you will be charged.
The host doesn’t monitor unmetered hosting. It means you can transfer unlimited amount for data but at a limited speed. So, in this case, the you aren’t charged for the data you use but are charged with a predictable flat rate.