Father Skywalker said:

What is the meaning of the title "the empire strikes back"???

It was taken from one of the early drafts of what was then known as "Episode 2". In it there was a new Sith lord that was trying to challenge Darth Vader's position. His name was Darth Back. At the climax there was to be an intergalactic boxing match. Darth vader represented the Empire and Darth Back represented himself. At the end of the match Back was beaten and Vader invited all the Imperial commanders to beat the crap out of Back, striking deadly blows. hence the original working title "The Empire Strikes Darth Back"