The inflation key instructs all the programs in the Inflation Accounting solution for Financial Accounting (FI) how to adjust for inflation a given G/L account.
You maintain inflation keys in Customizing for FI, by choosing Financial Accounting Global Settings → Inflation Accounting → Inflation Keys.
Once you have maintained the keys, you assign one at company code level to every G/L account that is to be adjusted.
In order to adjust accounts receivable and accounts payable, you assign an inflation key to the appropriate reconciliation account.
When you come to run the various inflation adjustment programs, they only adjust G/L accounts that you have assigned a key to. The key instructs the programs: