"Back in business"在英语中什么意思?是idiom么?and its origin?

"Back in business"在英语中什么意思?是idiom么?and its origin?

There are 2 different versions about it.One version says it is related to the Great Depression in American during which time people lost their jobs,and many of the companies in U.S.A was bankrupt.And this phrase was derived from the Great Depression when the stock started to climb and America came of it,because people can be back into what they were doing and the companies was back in business.And the other version can date back to 1880s when the Mighty Union Pacific Railraod Company went bust.But to everyone's surprise within less than a decade the company was reborn,with it's old name and racing along the tracks towards the future.So the Union Pacific Railraod was back in business.
\x05So,it can be used to mean a business that was going down is now back up.that's the original meaning of it.And with time went by,people started to use it in every aspects of life so "back in business " has become a figurative expressions with fixed meanings.
\x05This phrase can be used to mean that something is operating normally after having some difficulties.That means everything is good again/ back in order just like on my feet again.everything is up and running.Examples:
You were sick last week,but now you are well (back in business).Your inventory was stolen but you have re-stocked and you open again (back in business)You split up with your girlfriend and are dating again (back in business).
By the way,it is not an idiom,it is a slang but we also use it in formal situations.