FileVault

FileVault is a data encryption feature developed by Apple to protect user data in macOS. It was first introduced in 2003 as part of Mac OS X 10.3 (Panther).

Functionality
When activated, FileVault encrypts the user's home directory with a 128-bit  (AES), later upgraded to 256-bit with AES-XTS. It can automatically encrypt and decrypt on the fly while the user can continue to use the Mac.