Familiar, affectionate term for one's own mother, similar to 母ちゃん but with the polite prefix お. Used in casual family settings, especially by children or when speaking to children.
See also: 母ちゃん
Mum, what's for dinner tonight?
My mum is good at cooking.
Derived from 母 (かあ) with the familiar suffix ちゃん and the polite prefix お. The exact historical development is uncertain, but it is a natural affectionate variant of お母さん.