A call to action is a marketing term that refers to a prompt that invokes a response leading to a sale. When referring to a call to action (CTA) in the digital design world we usually mean the interactive element that leads to the next step in the experience – something that needs to be clicked or tapped.
To be obvious the call to action is interactive it would usually adopt a specific style to communicate to users this is what you do to proceed. This often takes the form of a button or link – the interactive element needs to look like UI. Most user journeys will have a CTA at each stage of the process.
To reduce confusion it is common to limit the number of CTA’s in any given page or area so that the choices presented to users are clear. If there are multiple choices it is sometimes necessary to differentiate which is the primary and which are the secondary calls to actions.