Google Hangouts is an instant messaging and video call service that is embedded in multiple Google web services and can be use as a web and mobile standalone app.
Google Hangouts was originally launched as a service embedded into Google+. Nowadays it could be accessed in several ways
- http://contacts.google.com (Preview)
- Chrome Extension for Google Hangouts.
- Chrome Desktop App for Google Hangouts
- Android app.
- iOS app.
It could be used to chat through instant messaging with users of Google Chat and third party chat clients and to have video calls with multiple participants. Video calls also could be enhanced by adding real time interaction apps.
While Hangouts on Air (tag google-hangouts-onair) was originally promoted by Google as the same app, its documentation is kept as part of the Classic Google+ Help Center and it still has its landing page inside the old Google+. For those reasons and due to its integration with YouTube, it should be considered as a different web app.