Know thy enemy. Anyway, the way I have defined lag and latency in game as this:
Lag: Any time you get the feeling of deja vu, matrix style. glichy, etc. (recommend that you move slowly in Halo 4 to get out of the sand trap that lag can be.)
Latency: Which is really 3 things and apparently the mother of all lag. I consider it the delay between actions and what happens on the sceen, probably because "Time-of-flight" and perhaps the fact you're playing against someone from North Korea or just really really far far away.
Oh and yes I have experienced lag. Must be the weather.
I was having problems when my xbox was hardwired with my internet. It's wireless now. Not so much anymore unless my Nat type fluctuates between Strict and Open.