Packet loss happens when one or more packets that are being sent across a computer network fails to arrive at the proposed destination. 

Packet loss occurs by faults in the transmission of data, commonly caused by Wi-Fi networks, network contention, server issues, internet provider faults, hardware faults, or hardware that has been set up incorrectly.

If you are affected by packet loss your connection may become unusable depending on the percentage of packet loss. A small amount of packet loss will impact all aspects of your internet usage, specifically audio and video quality.