In reply to Dudeski.

I would encourage you to have a look at http://wp-api.org/ which describes what WP REST API is and why it adds a significant improvement in the platform. But on the most basic level it allows a developer to interact with WordPress via a set of RESTful API.

That means I can create an application outside of WordPress (one created in JavaScript for example) and using RESTful approach interact with a WordPress installation using the API calls to get, update, etc. just the data I need instead of having to load WordPress in a WordPress template.
This greatly extends what can be done with WP and it provides a lot of options for developers and designers.