A customer, by our definition, must be actively paying you for your product or service on a recurring basis.

By this definition:

1) Someone who is fully discounted or credited for their subscription is not a customer.

2) Someone who is on a $0 subscription or trial is not a customer.

3) Someone who has a subscription starting in the future is not a customer.

4) Someone who is paying you through one-off charges rather than a subscription is not a customer.