a situation, quality etc which is as great as it can possibly be - used especially when talking about two opposites
The bacteria can withstand extremes of heat and cold.
In fact, the truth lies between the two extremes.
at the other/opposite extreme
At the other extreme is a country like Switzerland with almost no unemployment.
Advertisements seem to go from one extreme to the other (=change from one extreme thing to something totally opposite).
to a very great degree:
This kind of experiment seems cruel in the extreme.