In Microsoft Power BI, single-direction cross-filtering allows filters to flow in one direction—typically from dimension tables to fact tables—providing simpler and more predictable behavior. Bi-directional cross-filtering allows filters to flow both ways between tables and is mainly used in complex scenarios like many-to-many relationships, dynamic slicers, or bridge tables, but it should be used carefully because it can create ambiguity, slower performance, and unexpected filtering results.