外婆 (wàipó) means 'maternal grandmother' — specifically, one's mother's mother. The character 外 (outside) indicates the maternal side of the family in Chinese kinship terms. This term is widely used in southern China and informal speech.
周末我要去外婆家吃饭。
Zhōumò wǒ yào qù wàipó jiā chīfàn.
I'm going to Grandma's house for dinner this weekend.
外婆做的红烧肉最好吃了。
Wàipó zuò de hóngshāo ròu zuì hǎochī le.
The braised pork Grandma makes is the best.
小时候我经常住在外婆家。
Xiǎo shíhòu wǒ jīngcháng zhù zài wàipó jiā.
When I was little, I often stayed at Grandma's house.