Inverted Index

An Inverted Index is a data structure that maps each unique word or term to a list of all documents containing it, creating a reverse lookup system that enables efficient search queries.

The concept mirrors a book's index — just like when you look up 'polysemy' in a book's index to find page numbers, rather than reading every page. Search engines use this same principle to instantly locate relevant documents from billions of web pages without scanning each one individually.

Modern search engines use inverted indexes as their primary tool for lexical retrieval, where exact word matches are identified first. This word-matching step happens before semantic analysis in most search systems, allowing for rapid query processing across massive document collections.