A multimodal AI model announced by Google in May 2021, claimed to be 1,000× more powerful than BERT. MUM is multilingual (75+ languages), can process text and images together, and is trained to answer complex multi-step questions. It powers a growing share of Google features: improved snippet selection, "Things to know" boxes, and components of AI Overviews. Unlike a public API, MUM is used inside Google's stack — site owners can't directly optimise for it, but well-structured, comprehensive content with good imagery is the practical lever.