Humble term used when referring to one's own mother in formal or polite situations. Not used for someone else's mother.
See also: 父
My mother is out shopping right now.
母から教わった料理です。
This is a dish I learned from my mother.
I'm grateful to my mother for always raising me.
Even though I live far away, I want to take good care of my mother.
I gave carnations as a gift for Mother's Day.
お母様 politely refers to someone else's (or occasionally one's own) mother, while 母 is the humble term used to refer to one's own mother when speaking to others.
母 is the humble form used when talking about one's own mother to outsiders, whereas 母さん is the casual term used directly with or about her at home.
母 is the humble term used when referring to one's own mother in formal or outward-facing speech, whereas ママ is casual and affectionate.
mother (honorific)
mother's side of the family