Hello,
- A House Bank is a bank that is used by your company code (that's it, a bank where your company code has one of more accounts): House banks are defined at company code level and identified by a 5 digit code
- A House Bank Account is the account mentioned above: It is also determined at company code level and identified by a 5 digit code
- Bank key is the identification of a bank in your system irrespective of the fact that it is used as house bank and or as bank of a vendor/customer.
For more information's: Bank Master Data - Bank Accounting (FI-BL) - SAP Library
Good luck.
Th.