Drip marketing (aka. drip emails, or lead nurturing) is often used by modern marketers to nurture their leads through the sales funnel.

As others have mentioned the idea is to gain brand awareness and influence buyers through a regular series of targeted and relevant content or offers.

Typically for top of the funnel activities you might offer something like a general whitepaper or something which describes the overall business problems that your prospects might be feeling. From there you can use a marketing automation tool to send through additional material or reminders periodically depending on how your prospects engage with you.

The idea at the end of the day is to reduce that amount of direct time that a sales rep spends closing any deal by ensuring that leads have shown sufficient buying signals and are ready to purchase.