In the OSI Model's seven layers, a transmission control protocol (TCP). Which basically means, if a packet of information requested to be received gets lost and does not make it to it's destination. This protocol exists for the recievent user to request another packet of the one missing. This way no information is lost.
When this action cannot find the correct packet. This instance is called packet loss, and can cause many bugs and visual glitches in games or software needing the information from those packets.
