Access list (ACL)
An access list (ACL) is a set of extra permission rules on a file or folder, beyond its basic permissions. Storage Studio keeps them only where the drive can hold them.
An access list, or ACL (access control list), is a set of extra permission rules on a file or folder that go beyond its basic permissions — for example, letting one particular person on the Mac read a folder, or stopping anyone from deleting it. Adding people under Sharing & Permissions in a folder's Get Info window is one way they're created.
Most files don't have one, but shared folders and some app folders do.
When Storage Studio moves a folder, it keeps access lists if the destination drive can hold them — Mac formats such as APFS can. Some drives, such as exFAT ones, can't store them at all; there, Storage Studio leaves the access lists out rather than letting the whole move fail. The files and their basic permissions still arrive.
See also: What a move keeps · What to know about exFAT drives