What is Call To Action?

Legal Definition
In marketing, a call to action (CTA) is an instruction to the audience to provoke an immediate response, usually using an imperative verb such as "call now", "find out more" or "visit a store today".

A CTA can be a simple non-demanding request like "choose a colour" or "watch this video", or a much more demanding request. An obvious CTA would be requesting the audience to purchase a product or provide personal details and contact information.

Clever marketing strategies often combine a series of small CTAs. These smaller CTAs create a pattern of behaviour that makes it easy for the audience to follow-through with just one last CTA, completing a more demanding request, had it been asked without context. An example could be the purchase of a designer torch. The website might request the user choose a style, then a colour, a size and even a personalised engraving. When the user gets to see their personalised one-of-a-kind product, they are more likely to feel inclined to buy it as it rotates in full 3D rendered colour on their computer monitor or tablet.
-- Wikipedia
Legal Definition
Call to Action (CTA) is an organization that advocates for a variety of liberal causes to change the Catholic Church.