No. The turbochargers rotational velocity doesn't instantly drop to zero. Once the intake butterflies are back open and exhaust gas volume and velocity picks up the turbocharger is making boost again. You may be able to measure this delay, but that isn't turbocharger "lag". What people call "lag" is really boost threshold. It's the point in an engine's RPM curve at which the turbocharger can supply more air to the engine that it would have naturally. Natural in this case means atmospheric pressure. So 1 psi of boost is 1 psi above atmosphere. Likewise 1 bar of boost is twice atmospheric pressure.

I thought turbo charger was the delay in throttle response. That's what wikipedia seems to think too: http://en.wikipedia.org/wiki/Turbocharger#Turbocharger_lag

but I guess in the end I see what you are saying and it's merely a matter of terminology

Is what you're saying that the lag is actually the period before the turbo spins up and starts producing boost? In somewhat different wording, the lag is the engine running as if it were NA until the turbo can spin up to a speed that it will compress the incoming air? That's what I have always thought turbo lag is.