In Accounting for Nonprofits, you defined an account number made up of segments. The first segment was reserved for Fund, and a typical combination might have been: Fund- Account- Department. The account segment generally defined line items such as Cash, Fixed Assets, Accounts Receivable, Accounts Payable, etc.
Account Codes are the segment of the account number that defines what was previously referred to as the "account" (other names commonly used are the Post Code or Charge Code).
In The Financial Edge, Account Codes are defined in tables with short and long descriptions, and must remain consistent across funds. (For example, Account number 1000 cannot be "Cash" in Fund 1 and "Fixed Assets" in Fund 2). This consistency is essential for report creation and using the automatic account creation feature in The Financial Edge.
For more information, refer to The Financial Edge section of the Configuration Guide for General Ledger (PDF).