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 to find out more" or "visit a store today".
In web design, a CTA is a banner, button, or some type of graphic or text on a website meant to prompt a user to click it and continue down a conversion funnel. It is an essential part of inbound marketing as well as permission marketing in that it actively strives to convert a user into a lead and later into a customer. The main goal of a CTA is a click, or a scan in the case of a qr code, and its success can be measured via a conversion rate formula that calculates the number of clicks over the times the CTA was seen. Another way to test the effectiveness of a CTA is using A/B testing where several graphics are presented to a user and the graphic with highest success rate becomes the default.