Within a turbocharger's operating range, lag is the delay between the instant a car's accelerator is depressed and the time the turbocharged engine develops a large fraction of the power ava [..]

The time it takes the turbocharger to kick in after the driver accelerates; the lag results because a turbocharger compressor is spun by exhaust gases in the exhaust manifold.

A small delay in power delivery caused by the time it takes the turbo to spool up the turbine blades, thus creating boost. When the gas pedal is pressed, the engine revs up faster than the turbine blades. Hence, normal cars experience a small delay before extra power from turbo kicks in. The turbo is powered by the exhaust gases exiting the engine.

The lapse in time between the point when the accelerator pedal is depressed and the point at which the turbocharger produces boost pressure above atmospheric pressure.