The part of a marketing message that attempts to persuade a person to perform a desired action.
A call to action aims to persuade a visitor to perform a certain act immediately. "Buy Now!" and "Register Today!" are some common examples. The call to action is intended to improve the market’s response rate to the ad copy, as its absence may cause a visitor to forget about the ad and move on to other things.
Call to Action Buttons Best Practices Guide
UX Movement (February 21, 2011)
Secondary Calls to Action: Unsung Heroes of Persuasion
FutureNow (May 24, 2010)
Call to Action Buttons: Examples and Best Practices
Smashing Magazine (October 13, 2009)
10 Techniques for an Effective ‘Call to Action’
Boag World (January 22, 2009)