Trey Grainger discussed how search has evolved from basic keyword search to more advanced capabilities like understanding user intent, providing personalized search, and augmented search using machine learning and AI. He explained the concept of "reflected intelligence" where user interactions with search results are used to continuously improve search quality through techniques like signals boosting, learning to rank, and collaborative filtering. Grainger also outlined how knowledge graphs can help power semantic search by modeling relationships between entities to better understand queries and provide more relevant results.