Content Collections are simply indexes of content based on pre-defined search criteria or filters.
For example, Mura CMS can create an index of site content (Local Content Index) that has been flagged as "Featured" and categorized as "Domestic News" where the content resides under either the Blog or News sections of your site. This index typically consists of the Date, Title, Primary Associated Image, Summary, Credits, and Tags. You can control the maximum number of items you wish to display and more.
You can also broadcast these Local Content Indexes as RSS feeds (http://en.wikipedia.org/wiki/RSS), making it easy for visitors, or even other web sites, to consume information from your site and bring visitors back for details.
In addition to creating Local Content Indexes, Mura can also consume external RSS feeds and display pieces of that information on your site as well using the Remote Content Feed feature of Content Collections.