A call to action
The call to action button is a near cousin of the more basic button. In this case the call to action not only needs to be clicked, but it offers up a more compelling reason to do so. This collection of samples shows that a number of motivational factors can be leveraged when creating such design elements.
http://www.hongkiat.com/blog/call-to-action-buttons-guidelines-best-practices-and-examples/
