Virality

Growth that comes from existing users bringing in new ones through sharing, invitations, or visible use. Measured by the viral coefficient: how many new users each user brings.

When you'd see it: Product and growth discussions. A viral coefficient above 1 means each user brings more than one new user, and growth compounds without paid acquisition.

Why it matters: Virality is the cheapest growth there is because users do the acquiring. Few products are genuinely viral, and engineering a viral loop is much harder than hoping for one.