Literally: a cold hurricane.

Some people misuse the term to mean "a blizzard affecting New England and/or the Northeast", but it actually specifically refers to a storm that's been pushed inland by sea winds coming from the northeast, off the Atlantic Ocean. That specific pattern results in a particularly cold and brutal storm.

Nor'easters are technically cyclones, just like hurricanes, and the two are very similar in many regards. The difference is that a Nor'easter forms further north, in cold water, and it is actually strengthened by cold air, whereas hurricanes form further south and are diminished in strength as they cool off.

https://scijinks.gov/noreaster/