"Mom" was brought to America in the 1860s and is usually considered an American word. However, the British English speakers of the Midlands also use "mom" and not "mum."

"Mum," according to Online Etymology Dictionary, is a "pet name" for "mummy" and dates back to the 1820s. In 1957, sociologists in Great Britain used "mum" as "the working class mother as an influence in the lives of her children."