The customer lifecycle is the staged model of a customer's relationship with a company from first awareness through purchase, retention, expansion, and advocacy or churn. The full stages span first awareness, evaluation, purchase, onboarding, ongoing use, expansion, and advocacy, used to organize marketing, sales, product, and customer success efforts around the right intervention at the right stage. It is the structural model that lifecycle marketing operates against and the conceptual loop that has been replacing the linear funnel in modern go-to-market thinking.
The canonical stages most companies adapt: awareness (prospect first encounters the category or brand), consideration / evaluation (active research, comparison...