Final answer:
Transparent Data Encryption (TDE) is the feature that encrypts on-premises SQL Server databases.
Step-by-step explanation:
The feature that encrypts on-premises SQL Server databases is called Transparent Data Encryption (TDE).
TDE is a security feature in SQL Server that helps protect sensitive data by encrypting data at rest. It is used to protect the physical files of a database, including the database data file, log file, and backup files.
When TDE is enabled, the database files are encrypted and can only be accessed by authorized users with appropriate encryption keys. This helps to prevent unauthorized access to the database files and ensures that the data remains encrypted even if the physical storage media is stolen.