What is the difference between data at rest, data in transit, and data in use?

Data at rest is stored data residing on hard drives, databases, backups, or removable media, protected primarily by encryption, access controls, and physical security. Data in transit is data moving across networks, protected by transport encryption protocols like TLS, VPNs, and IPsec. Data in use is data being actively processed in memory or CPU registers, which is the most difficult state to protect because it must be decrypted for processing. Emerging technologies like homomorphic encryption and secure enclaves address data-in-use protection.