Reblogged from Google Apps Update
Every collection is a focused set of posts on a particular topic, providing an easy way for people using Google+ to organize their interests and focus areas. For Google Apps customers, collections could be used for communicating to a project team or organizing an event, allowing followers to easily access all relevant posts in one location.
Each collection can be shared publicly, privately, or with a custom set of people. Once you create your first collection, your profile will display a new tab where other people can find and allow your collections. Posts in collections you follow will appear in your Home stream, with a link to easily jump right into the collection so you can get a similar content from that author.
Collections is available on Android and the web, with iOS coming later.