姨婆 is a kinship term that refers to the sister of one's grandparent — specifically, the aunt of one's parent. It can be your mother's aunt (your maternal grandmother's sister) or your father's aunt (your paternal grandmother's sister), depending on the family context. In spoken Chinese, clarifying which side of the family (e.g., 奶奶那边的姨婆 or 外婆那边的姨婆) is often helpful, as the term alone does not specify maternal or paternal.