Packet loss
Data that never arrives at its destination and has to be retransmitted, or is simply lost.
Small amounts are normal and invisible for file transfers because the protocol retransmits. Real-time traffic cannot wait for retransmission, so loss shows up directly as choppy audio and frozen video.
Persistent loss usually points at a physical problem, a failing cable or port, or a saturated link, and it is worth chasing rather than tolerating.
Where this comes up
Packet loss sits inside our networks and infrastructure work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.
Related terms
Latency The delay between sending data and it arriving, usually measured as a round trip in milliseconds. Quality of service Prioritizing certain network traffic so that latency-sensitive applications stay usable under load. Network monitoring Continuously checking that devices, links, and services are up and performing as expected.