A lexical database is a structured collection of words and their meanings, relationships, and usage. It serves as a resource for understanding language by providing information about synonyms, antonyms, and other linguistic features. One well-known example of a lexical database is the WordNet, which organizes English words into sets of synonyms and describes their meanings. These databases are useful in various applications, including natural language processing, linguistics, and artificial intelligence. They help computers understand human language better by providing context and relationships between words, making them essential tools for tasks like machine translation and text analysis.