Customers and Business Partners 
Definition
A company deals with different natural and legal persons during business transactions: A customer orders goods from your company. A forwarding agent might deliver goods to the customer. An employee within the company processes the business transactions. All roles a natural or legal person can assume are represented by business partners in the SAP System.
Business partners
A company has contact with its business partners, who are customers and vendors. Data on each of these and on the company's personnel is stored in a separate master record.
Customers
The term “customer” is used to define all customers to whom the company has contact. The term “vendor” is used to define all business partners who carry out a delivery or a service for the company. A business partner can be a customer and a vendor at the same time if, for example, your customer also supplies goods to you. In this case, both a customer master record and a vendor master record must be created for the business partner. You can create a link between the master records by entering the vendor number in the customer master record and the customer number in the vendor master record.
Vendors
Data on business partners who are vendors, for example, forwarding agents, is managed in the vendor master record. If a vendor is also a customer, a link can be created.
Personnel
Data on employees of your own company, for example, sales personnel or clerical staff, is managed in the personnel master record. Data on each employee can be managed by his or her personnel number.
Only the personnel department of your company is authorized to create a personnel master record, using Human Resources (HR). The personnel department of your company manages the personnel numbers of the employees. If HR is not used in your company, you can create a personnel master record yourself for employees in sales and distribution.
See also:
Logistics –
General: 
Master Data Business
Partners
Partner Determination in Sales and Distribution