This document discusses query understanding in search engines. It describes how query understanding involves identifying entities and tags in queries, predicting the user's intent or topic area, expanding queries using related terms, and incorporating spelling corrections. The key aspects of query understanding covered are tagging queries for entities like names, titles, companies; predicting the user's vertical intent like jobs, people or companies; and expanding queries using name synonyms, job title synonyms or signals from past user queries and clicks. The document also suggests giving users more transparency, guidance and control over the search process.