An "autoresponder" is an automated email message, or a series of email messages sent in response to an action a prospect or subscriber has taken. When set up in a series to drip over a specified amount of time, autoresponders are also often referred to as a "drip campaign" or "drip marketing."

As an example, an autoresponder can be set up to send immediately after the person signs up to your list. You might then schedule another autoresponder to send three days later, offering a related whitepaper or access to on-demand webinar.  

To learn more about about autoresponders and ideas on how to use them, check out the following blog articles: