妈 (mā) is an informal noun meaning "mom" or "ma." It is a shortened form of 妈妈 (māma) and is commonly used in casual speech when calling out to or referring to one's mother.
妈,今天晚饭吃什么?
Mā, jīntiān wǎnfàn chī shénme?
Mom, what's for dinner tonight?
妈说她下午要去超市买菜。
Mā shuō tā xiàwǔ yào qù chāoshì mǎi cài.
Mom said she's going to the supermarket to buy groceries this afternoon.
我妈做的红烧肉是世界上最好吃的。
Wǒ mā zuò de hóngshāoròu shì shìjiè shàng zuì hǎochī de.
The braised pork my mom makes is the most delicious in the world.