What is Transparent Data encryption for Azure SQL Database?

Transparent data encryption (TDE) helps protect Azure SQL Database, Azure SQL Managed Instance, and Azure Synapse Analytics against the threat of malicious offline activity by encrypting data at rest. It performs real-time encryption and decryption of the database, associated backups, and transaction log files at rest without requiring changes to the application. By default, TDE is enabled for all newly deployed Azure SQL Databases and must be manually enabled for older databases of Azure SQL Database. For Azure SQL Managed Instance, TDE is enabled at the instance level and newly created databases. TDE must be manually enabled for Azure Synapse Analytics.