姥姥

Chinese splits your grandmothers by which parent they came from, so there is no single word for grandma. Your mother's mother is 姥姥, and your father's mother is 奶奶. The grandfathers follow the same logic: 姥爷 is your mom's dad, and 爷爷 is your dad's dad. The 姥 character marks the mother's side, which is why 姥姥 and 姥爷 share it. When you talk to her face to face, you just call her 姥姥 — that's the address term too. “妈妈的妈妈叫姥姥。” (Mom's mom is called 姥姥.) ── [《我的家人（1）》](/read/my-family-members-1#s8)

姥姥 is everyday northern speech, especially around Beijing, while 外婆 is what people say in the south and in Taiwan. Both words mean exactly the same person, so nobody will misunderstand you either way. The stiff written version is 外祖母, which shows up in essays, news, and official paperwork. If you learned with Taiwanese apps or textbooks, 外婆 is probably the word that got drilled into you first. Speak whichever one fits your city, but recognize all three when you read.

姥姥 is a family-tree word, not a generic polite way to greet old people. Calling a stranger 姥姥 tells her she is your mother's mother, which sounds genuinely weird. For an elderly woman you don't know, northerners say 奶奶 or 大妈, and southerners often reach for 阿姨. Once you actually know her, like a friend's grandmother or a neighbor, 姥姥 is warm and completely normal. It's about real relationship, not about age.

Repeated family words drop the tone on the second syllable, so 姥姥 comes out as lǎolao with a light second beat. The same thing happens in 奶奶 nǎinai, 妈妈 māma, 爸爸 bàba, and 弟弟 dìdi. Learners who say lǎolǎo with two full third tones sound like they're reading a dictionary entry aloud. There's no special rule to memorize here — it's simply how doubled kinship words behave. Copy a native speaker's rhythm and you're done.