YQL (Yahoo Query Language) allows users to query and manipulate data from various data sources on the web using SQL-like statements. It can be used to select, insert, update, and delete data from HTML, XML, JSON, RSS, Atom, and Microformats. YQL also allows creating custom "Open Data Tables" to store and manage data from different sources. The API has a daily limit of 100,000 calls but additional limits can be requested.