Combustion lag refers to the time between spark(ignition) and the highest combustion pressure in an engine.

Ignition timing refers to how many degrees before top dead center(top dead center compression in 4 strokes) the crankshaft rotation is during ignition.

These two are connected by timing your ignition on point with combustion lag characteristics to tune ignition timing and gain max volumetric efficiency out of an engine.

Timing advances (ignites farther from tdc) as rpm's increase.

it is same as ignition delay. it is the time gap between the injection of fuel and the first particle of mixture which get ignited

Fredric B. Clarke has written:

'A study of the ignition lag of spontaneous rocket propellants' -- subject(s): Combustion, Fuel, Rockets (Aeronautics)

Inside lag is the time to implement (pass) a policy, while outside lag is the time it needs to take effect.