In sales and marketing, lead nurturing is the process of building relationships with qualified sales prospects regardless of their timing to buy. Your goal is to earn their business when they are ready to purchase. Many of your lead-generation tactics will be very top-of-funnel, meaning you're hopefully casting a wide net and generating a lot of new leads.
Because of modern buying habits, however, the majority of those new sales leads aren't ready to make a purchase because they're still researching options. Without a process like lead nurturing, your lead-generation efforts are dead in the water, meaning you're missing a huge opportunity for your lead-generation efforts to convert to revenue.
Through lead nurturing, you can provide relevant material that maps directly to each phase of the buying cycle, persona, and interests. Basically, lead nurturing plugs your leaky funnel!
You can't just send your leads a series of unrelated emails without context. You have to listen to signals across all of the channels they spend time on, and engage your leads based on their interests.