Actually it is just a place ruled by an emperor. Sometimes they are used incorrectly e.g Red Empire in Eastern Europe, the Persian Empire e.t.c
It is often used now to define one country which forces other countries to serve it by force and oppresion, this I would not put as a correct term as it includes superpowers and would therefore make this term invalid.
Rome was the first true empire as the term came from the military title imperartor
Something that is immortalised but is in actually fact rubbish.
"I wonder what happened to the Beagle 2 probe"
"Darwin sailed on the Beagle, a ship which was eventually used as a staionary ship in a vain attempt to stop summugling"
"You see that Beagle, what tricks can it do?"