Unmetered hosting (50mbit sec) is a hosting plan where the traffic is not measured, but there is a speed limit. You can have as much traffic (data) as you want, but the traffic can only travel at speeds of up to 50mbps.
You will not be charged for the traffic sent to and from your server during the month. However, you will be charged extra for internet traffic if your incoming data (downloads) is more than 33% of your total traffic. This is based on the ratio of outgoing to incoming data. If you exceed the ratio of 2 parts sent for every 1 part received, you will be charged the extra traffic rate based on the full amount of data you use, both incoming and outgoing.