曾祖母是爷爷或者奶奶的妈妈，也就是你爸爸的奶奶。

A 曾祖母 is the mother of your grandfather or grandmother, that is, your father's grandmother.

这个词比较正式，很多人平时会叫她“太奶奶”。

This word is more formal; many people usually call her “太奶奶.”