Latency, even if it isn't enough to cause hitches. Idiots started calling low performance "lag," but they are wrong. In Quake III Arena, if I missed you with a rail shot that would have connected in LAN play, I say that it's lag. If everything hitched and youfroze for a second, allowing me to nail you due to network performance, that's "lag" as well. You lag behind and the mercies can tolerate it to a certain extent, but it's lag none-the-less.