Packet loss
Also said as Dropped packets, Loss
Some of what you send simply never arrives. Each game has to choose: ignore it, wait for it to be sent again, or send things in a way that makes it not matter.
Waiting holds up everything behind the missing packet, and that stall is why action games avoid the internet's reliable protocol, TCP, for movement. Ignoring it leaves machines disagreeing for good.
Say it
“Do not resend inputs. Every packet carries the last eight inputs, so a player can lose one packet in ten and nobody notices.”
Where you’ve seen it
Quake III avoids TCP entirely. Each update is a difference from the last update that client confirmed, so whatever got lost is automatically included in the next one.
Not to be confused with latency
Latency is data arriving late. Loss is data not arriving at all. Resending turns loss into latency, and a big spike of it.