Generation creates the lead; Nurturing drives the lead down funnel.
Lead generation could be defined as attracting target audience attention, acquiring the target audience, and formally converting the audience into an active lead. The objective of Online Advertising is to generate leads (as defined). Once a lead is generated, the lead instantly enters the lead nurturing phase of the customer journey.
Lead nurturing involves building relationships with prospects with the goal of ultimately driving the lead toward the final desired action (for example, submitting an application). Lead nurturing can be accomplished in many ways, but always entails a timely, targeted approach to connecting with leads in order to fulfill audience needs at each step of their journey, and progress the lead down the funnel toward conversion (some examples include sharing additional program information, inviting leads to participate in webinars or events, setting up informational sessions, sending resources via email drip campaign).
Each should ultimately be refined by the team and ultimately each phase should be mapped according to the target persona, and in this case, by the program.