In certain forms like sales orders, sales invoices , you have access to an object called customer_bill_to. This object represents a customer record.
Here are the fields available for customer_bill_to
id: An id that represents the customer.
party: An object that mostly contain contact information for the customer. See party object.
currency: The default currency being used by the customer. See currency object.
public_custom_fields_list: A list of public custom fields related to the customer. See custom_field object