Standard Entry Class Codes, or SEC Codes, are all the valid payment methods as prescribed by NACHA.  Each SEC Code defines the type of transaction (debit or credit), type of account (corporate or consumer), and any information specific to the format (such as single/recurring, terminal location, or check number).

 

The most common SEC Codes are CCD and PPD, which are credits and debits done against corporate and consumer accounts respectively.  These are used for direct deposit, payments to vendors, and collections from customers.