Web SQL Database is a web page API for storing data in databases that can be queried using a variant of SQL.
The API is supported by Google Chrome, Opera, Safari and the Android Browser.
The W3C Web Applications Working Group ceased working on the specification in November 2010, citing a lack of independent implementations (i.e. the use of a database system other than SQLite as the backend) as the reason the specification could not move forward to become a W3C Recommendation.
Mozilla Corporation were one of the major voices behind the break-up of negotiations and deprecation of the standard, while at the same being the main proponents behind an 'alternative storage' standard, IndexedDB.
References
Web SQL Database Wikipedia(Text) CC BY-SA