This is a bit of legacy from Apple’s Pre-Mac OS X systems: files or folders could be set invisible (via software like FileBuddy) or locked (via the Finder)…

In Mac OS X, if you have installed Apple’s free developer tools, these contain a command line utility to manipulate HFS+ attributes:

which setfile ; setfile -h
Usage: SetFile [option...] file...
-a attributes # attributes (lowercase = 0, uppercase = 1)*
-c creator # file creator
-d date # creation date (mm/dd/[yy]yy [hh:mm[:ss] [AM | PM]])*
-m date # modification date (mm/dd/[yy]yy [hh:mm[:ss] [AM | PM]])*
-P # perform action on symlink instead of following it
-t type # file type

Note: The following attributes may be used with the -a option:
A Alias file
B Bundle
C Custom icon*
D Desktop*
E Hidden extension*
I Inited*
M Shared (can run multiple times)
N No INIT resources
L Locked
S System (name locked)
T Stationery
V Invisible*
Z Busy*

Note: Items marked with an asterisk (*) are allowed with folders
Note: Period (.) represents the current date and time.
Note: [yy]yy < 100 assumes 21st century, e.g. 20yy

See also man SetFile