In A Christmas Carol, what does "offal" mean?
Your question refers to a description of the setting in chapter four when the Ghost of Christmas Future takes Ebeneezer Scrooge to view a future scene in a sort of pawnshop, where Scrooge's former employees are selling property that they have looted from future-Scrooge after he died. The shop is in a seedy part of town and is "a low-browed, beetling shop, below a pent-house roof, where iron, old rags, bottles, bones, and greasy offal, were brought".
In this context, offal actually refers to leftover body parts of some kind of animal. The description continues with a remark about the "mountains of unseemly rags, masses of corrupted fat, and sepulchres of bones" that are present in the shop. The rotting fat and piles of bones are clearly what Dickens was referring to when he used the word "offal".
In Victorian times men known as rag-and-bone men or rag-gatherers would scavenge all over London looking for anything that they could resell. Salable items included bones and even grease from animal carcasses, since both of these could be put to use by people. The grease could be used in making soap, and the bones could be used for a variety of purposes. It makes sense, then, that offal would be present in the shop where the charwoman and the laundress have come to hawk Scrooge's belongings. Offal was just another commodity in which the shop's proprietor, old Joe, would have trafficked.