Extended over water allows an aircraft to fly beyond 50NM from the coast line.
ETOPS = Extended Twin engine operations.
This allows an operator to fly a twin engine aircraft greater than one hour at single engine cruise speed from an alternate airport. There are different tiers of ETOPS, 120 minute and 180 minute. This does not apply to three and four engine aircraft.
A MEL for an ETOPS aircraft is a lot more stringent than for a non ETOPS. It is possible for an aircraft to be still airworthy but downgraded to non ETOPS compliant. Also maintenance intervals for ETOPS aircraft are more frequent.
-Keep the dirty side down