A CTA is a call to action that aims to get an immediate response from the person who reads or hears it. A call-to-action is a fixed part of online marketing.
A call-to-action tries to get the user to take a specific action. For example, filling out a form, submitting an order, clicking on a teaser, signing up for a newsletter, or opening a link.
Most CTAs appear in the form of a button to get the user's undivided attention and not be overlooked. Within an online marketing concept, call-to-actions are used to guide the user through the user journey in the most targeted way possible.