Hangouts are a Google+ service which are used to video, voice, or text chat with other people. Hangouts are integrated with nearly all of Google's services, including Google+, YouTube, Google Drive, Android, and Gmail. The video hangouts are compatible with certain applications that are specially designed for it. Some of these applications can do things such as display videos, animations, or other screens, or they can interact with certain web pages to help with productivity. A list of applications available for hangouts can be found here.