What does "encryption at rest" refer to?

Encryption at rest specifically refers to the practice of encrypting data while it is stored on a physical medium, such as a hard drive, SSD, or any other storage device. This is an essential security measure that protects sensitive information from unauthorized access and breaches when the data is not actively being accessed or transmitted.

When data is encrypted at rest, even if someone gains physical access to the storage medium, they would not be able to decipher the data without the correct decryption key. This is particularly crucial for safeguarding data in environments that may be susceptible to theft, loss, or unauthorized access, such as cloud storage services or enterprise databases.

Other alternatives, such as encrypting data in transmission, focus on protecting data while it is moving across networks and during transmission between systems. The concept of encrypting data during processing deals with securing the data while it is being used or acted upon, and encrypting data during user access pertains to protecting data while users are interacting with it. Each of these practices addresses different phases of data security, but they do not capture the essence of what encryption at rest entails.