After birthday and mothers day cards, my Mom told us that she doesn't like us to use the spelling 'Mum'. When I asked why, she said it's a cut down term from 'Mother' so to remain with the trend it's more correct to use 'Mom'.
This one.
mum is correct, however i use ma to amuse myself
wikipedia said:The proverbial "first word" of an infant often sounds like "ma" or "mama". This strong association of that sound with "mother" has persisted in nearly every language on earth, countering the natural localization of language.