Business Partners 
The Business Partners module manages all the information relevant for your relationships with customers, vendors, and leads (interested parties), as well as performing and reviewing internal reconciliations for business partners.
Example
Typical information includes contact persons, addresses, payment terms, and financial and logistic information.
Business Partners and Accounts
SAP Business One differentiates between business partners and G/L accounts:
Business partners are all your company customers, vendors, and leads.
G/L accounts are all the entities defined in your company's Chart of Accounts, such as expenses, revenues, assets, and liabilities.
SAP Business One connects between business partners and G/L accounts through control accounts that are defined during system initialization, and which may vary for different business partners.
All sales and purchasing transactions are posted to the appropriate control accounts, allowing you to access the overall balance, the balance for customers, and the balance for vendors in one G/L account. In addition, you can access the balance of a specific customer or vendor.