XIRR stands for Extended Internal Rate of Return. It's a financial metric used to calculate the annualized return of an investment that has irregular cash flows (deposits, withdrawals, dividends) occurring at different points in time. Unlike regular IRR, XIRR accounts for the timing of cash flows, providing a more accurate measure of performance, especially for investments with uneven cash flow patterns. XIRR is a valuable tool for investors evaluating complex investments or portfolios.