American English has no mould, and British English has no mold. In other words, the word referring to (1) the various funguses that grow on organic matter or (2) a frame for shaping something is spelled the same in both uses, and the spelling depends on the variety of English.
Of course, the spelling difference extends to derivatives such as moldy/mouldy and molding/molding and to the verb sense to shape with a mold.
Australian and Canadian English favor the British spelling, though mold is fairly common in Canadian publications.
Inside, the rain had spawned black, green, and yellow mold that crawled the walls. [Atlantic]
Obama has been more in the mold of George H.W. Bush and his secretary of state. [Daily Beast]
If some of the insulation is intact, leave it in place unless it is moldy. [Boston Globe]
Outside the U.S.
Without air conditioning in a highly humid climate, mould could form. [Montreal Gazette]
And Pretty Ballerinas is still making shoes in the mould of the original pair created in 1918. [New Zealand Herald]
There’s no bread, and even the mouldy cheese has been chipped away at. [Scotsman]