1. Maternal Aunt: This is the most common meaning. In India, "chachi" refers to the sister of your mother.
2. Elder Sister-in-law: In some regions, "chachi" can also refer to the wife of your father's younger brother (i.e., your younger uncle).
3. Respectful Term: It can be used as a general term of respect for an elderly woman who is not a close relative.
4. Informal term: It can be used informally as a friendly term of address for any woman.
The exact meaning of "chachi" depends on the context and the specific family relationship.