The short answer is that they are identical in meanings. They both refer to the process of injection molding/moulding, both refer to the trim molding/moulding around your home floors and both refer to the undesirable black fungus mold/mould. Mold is the American English spelling and Mould is British. Normally Canada adopts the British “ou” spelling like colour v.s. color … but in the case of Mold/Mould Canadians have generally adopted Mold.