What do you call your mothers sister in Arabic?

In Arabic, you call your mother's sister "خالة" (khala). This is the most common term and applies to both your mother's sister and your father's sister.

However, you might also use the term "عمّة" (amma) if you are specifically referring to your father's sister. While "khala" can be used for both, "amma" is more specific to your father's side.