A network administrator deploys an FDE solution on all end user workstations.

Full-disk encryption (FDE) protects the contents of storage media, which is a classic data-at-rest control. The Study Guide explains the “three situations” relevant to confidentiality—at rest, in transit, and in use—and then specifically ties disk encryption/FDE to protecting stored data: “Data at rest, or stored data, is that which resides in a permanent location awaiting access… Examples… hard drives…” It then describes FDE as an encryption method applied to disks: “Full-disk encryption (FDE) is a form of encryption where all the data on a hard drive is automatically encrypted, including the operating system and system files… In the case of loss or theft, FDE can prevent unauthorized access to all data on the hard drive.”

That is exactly the definition of protecting data at rest—it is intended to prevent disclosure if a laptop/workstation is lost, stolen, or the drive is removed. This is not masking (hiding parts of fields), not data in transit (network encryption like TLS/VPN), not obfuscation (making code hard to understand), and not data sovereignty (jurisdiction/location requirements). Therefore, deploying FDE on workstations is a data-at-rest protection strategy.