What is the meaning of Duff?

Dough.

A stiff flour pudding, often with dried fruit, boiled in a cloth bag, or steamed.

A pudding-style dessert, especially one made with plums.

Decaying vegetable matter on the forest floor.

Coal dust, especially that left after screening or combined with other small, unsaleable bits of coal.

Fine and dry coal in small pieces, usually anthracite.

A mixture of coal and rock.

The bits left in the bottom of the bag after the booty has been consumed, like crumbs.

Something spurious or fake; a counterfeit; a worthless thing; a defective thing.

An error.

Worthless; not working properly, defective.

The buttocks.

To disguise something to make it look new.

To alter the branding of stolen cattle; to steal cattle.

To hit the ground behind the ball.

Alternative form of daf (type of drum)

dull (not shiny)

Source: wiktionary.org