A response rate is a metric which represents the number of people who engage with a call to action (CTA). It can refer to a literal response, in the sense of a prospect replying to an email marketing message. However, just as often a response rate is aiming to measure the behavior of a prospect after being presented with a CTA. If, for example, the call to action is to fill out a survey, the number of people who do so increase the response rate. This is true even though the prospects haven’t actually “responded” to the company.