Mother — a colloquial term for one's own mother, commonly used by children or in familiar contexts.
母さん、今日のお弁当ありがとう。
Mom, thanks for today's lunchbox.
うちの母さんは料理がとても上手だ。
My mother is very good at cooking.
子どもが『母さん』と呼びかけた。
The child called out, 'Mom.'
Colloquial use meaning 'wife' — sometimes used by a speaker to refer to his own wife (usage depends on region/generation).
彼は冗談で自分の妻を『母さん』と呼んだ。
He jokingly called his wife 'mom.'
親しい間柄では『母さん』が妻を指すこともある。
Among close circles, 'kaasan' can sometimes refer to one's wife.