What is the meaning of "DFKK" at the beginning of SAP FI-CA tables ?

Many important tables in SAP FI-CA use the same naming convention whereby they start with "DFKK". Examples

DFKKKO: Header Data in Open Item Accounting Document
DFKKOP: Items in contract account document
DFKKOPK: G/L Items in contract account document
DFKKOPW: Repetition Items in contract account document
DFKKSUM*: Documents transferred to General ledger (reconciliation keys)

From looking at other modules, I would say "D" and "FKK" stand for separate things but it would be helpful to relate a meaningful business term to these abbreviations. Does anyone know (or at least have a good guess...) what they stand for ?