In Odoo, a contact refers to an individual or organization that you have a relationship with, but they may not necessarily be a customer. A customer, on the other hand, is someone who has made a purchase or transaction with your business.

In the CRM module, the "Contacts" feature allows you to store and manage all the contact information for individuals and organizations that you have a relationship with, whether they are customers or not. The "Customers" feature, on the other hand, is specifically for managing information about customers who have made a purchase or transaction with your business.

In the Sales module, the "Contacts" feature allows you to create, edit, and manage the contact information of your customers, partners, suppliers, and other parties you do business with. The "Customers" feature is used to manage your customer's information and keep track of their orders and invoices.

In summary, a contact is a general term used to refer to any individual or organization you have a relationship with, while a customer is a specific type of contact who has made a purchase or transaction with your business.