The percentage of signed-up users who successfully complete a predefined set of key actions representing the core value (the Aha moment).
Why it matters: A high sign-up rate means nothing if activation is low. Improving activation is usually the highest leverage growth activity a startup can do.
In practice: If 1,000 users sign up for a CRM, but only 200 import a contact list (the activation metric), the activation rate is 20%.