Google Closure Tools is a set of tools to help developers build rich web applications with JavaScript

JavaScript

JavaScript is a prototype-based scripting language that is dynamic, weakly typed and has first-class functions. It is a multi-paradigm language, supporting object-oriented, imperative, and functional programming styles....

. It was developed by Google

Google

Google Inc. is an American multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, and generates profit primarily from advertising through its AdWords program...

 for use in their web application

Web application

A web application is an application that is accessed over a network such as the Internet or an intranet. The term may also mean a computer software application that is coded in a browser-supported language and reliant on a common web browser to render the application executable.Web applications are...

s such as Gmail

Gmail

Gmail is a free, advertising-supported email service provided by Google. Users may access Gmail as secure webmail, as well via POP3 or IMAP protocols. Gmail was launched as an invitation-only beta release on April 1, 2004 and it became available to the general public on February 7, 2007, though...

, Google Docs and Google Maps

Google Maps

Google Maps is a web mapping service application and technology provided by Google, free , that powers many map-based services, including the Google Maps website, Google Ride Finder, Google Transit, and maps embedded on third-party websites via the Google Maps API...

.

Closure Compiler

The Closure Compiler is a JavaScript optimizer that rewrites JavaScript code to make it faster and more compact.

Closure Library

The Closure Library is a JavaScript library, written specifically to take advantage of the Closure Compiler, based on a modular architecture. It provides cross-browser functions for DOM manipulations and events, AJAX and JSON, as well as more high-level objects such as User Interface widgets and controls.

Closure Templates

Closure Templates are a templating system for dynamically generating HTML in both Java and Javascript.

Because the language was apparently referred to as "Soy" internal to Google, and "Soy" remains in some of the documentation and classes, sometimes Closure Templates are referred to as "Soy Templates".