Describe the AARRR funnel.

The AARRR funnel is a user journey analysis model in a product, consisting of five stages:

1. Acquisition — how users learn about your product (advertising, SEO, social media).
2. Activation — the first positive experience of the user when they start using the product and receive value.
3. Retention — bringing users back and regular use of the product.
4. Referral — users recommend the product to others.
5. Revenue — monetization of users when they make purchases or generate income.

This model helps understand at which stages users are lost and where to improve the product or marketing.