CLOSED LOOP
This uses a lambda sensor to detect the air/fuel ratio (mixture).
If it senses the mixture is slightly rich then it leans off the map and visa-versa.
This only happens for idle and light loads if using a narrow band sensor type.
If a wide band type is used then the ecu can adjust throughot the map all the time.

WASTED SPARK
On conventional cars there is a distributor that has mechanical moving parts to delivery the spark to the right spark plug.
Th rotor arm in the dizzi doesnt touch the connections so inside the cap, a spark jumps from the rotor arm to the selected spark plug.
This makes the spark at the plug weaker and also the dizzi is sensitive to miosture.

On a wasted spark system, 2 coils are used instead of 1.
One coil fires plugs 1 and 4 at the same time, the other coil fires 2 and 3 at the same time.
As there are 2 coils, the ignition system has twice as long to charge them so can produce bigger sparks.
Also, there are no moving parts to waer out and no sparks outside the cylinder.
Bigger sparks mean better idle and and smoother running and helps towards saving fuel and emissions.

Its called wasted spark because 2 plugs are fired all the time and so 1 is wasted as only 1 cylinder is actually firing due to it having a fuel mixture.
This is ok as when 1 cylinder is on the firing stroke the other is always on the exhaust stroke.