Engagement is the umbrella for how much and how meaningfully viewers use a service: how often they return, how long they watch, how many titles they explore, and how deeply. It is the behavioral layer between acquiring a user and keeping them, and it is the strongest leading indicator of retention.
Services track engagement through metrics like watch time, sessions per week, titles per user, and completion, often segmented into cohorts and engagement tiers (a viewer watching most days behaves very differently from a monthly drop-in). Because engaged viewers churn far less, almost every product investment - recommendations, content, QoE, notifications - is ultimately judged by its effect on engagement.
