Simon is on point here. Drip marketing is essentially what companies like Salesforce and Infusionsoft offer. Is part of CRM offerings, realistically speaking there is no guarantee that you will close (whatever your goal is) each click through your website or landing page or phone number... drip marketing is used so that once you have secured contact information, typically emails, you can nurture them.
After a few emails, assuming they haven't unsubscribed, you would benefit from moving that group who hasn't acted or clicked on your email links (mailchimp.com provides the feature of seeing reader's actions) onto a 'nurture phase' which is just you deciding how long to delay their next emails to.. could be emailing once a week, once a month now or once a year. It works because on average a leisure consumer requires about 18 interactions with your brand before being comfortable enough to jump on your offerings. Even if you email once a month, the next time they have an immediate need for what you offer you should be the first thing that comes to their mind. Is called drip by some because it helps you trickle in new customers lol.
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