Complex sentence: In the United States, bank reserves are held as FRB (Federal Reserve Bank) credit in FRB accounts; they are not separated into separate "minimum reserves" and "excess reserves" accounts.
Split into simpler sentences: In the United States, bank reserves for a commercial bank are held in part as a credit balance in an account for the commercial bank at the applicable Federal Reserve bank (FRB). This credit balance is not separated into separate "minimum reserves" and "excess reserves" accounts.