What does the word "business" mean in Marley's words?

I am assuming you are talking about the part where Marley's ghost is talking to Scrooge and Scrooge tells him he was always "a good man of business."

At that point, Marley's ghost says:

'Business!' cried the Ghost, wringing its hands again. 'Mankind was my business. The common welfare was my business; charity, mercy, forbearance, and benevolence, were, all, my business. The dealings of my trade were but a drop of water in the comprehensive ocean of my business!'

What Marley is saying is that his business should have been people.  He should have cared more about them and less about making money.  He says that his and Scrooge's firm was really just a little thing compared to what he should have been concerned about.

So the word seems to mean what Marley should have cared about as opposed to the company that he and Scrooge owned which was what he really did care about while he was alive.