'Lag' is an unusually great delay between event A and B. Like network lag where you stop receiving data for a few ms or more, or input lag if you're running with triple buffering without the power to run it properly, or just a shitty computer being unable to process data fast enough and getting framerate lag.
Regular/reasonable latency is not referred to as lag in this context.
Regular/reasonable latency is not referred to as lag in this context.