"Hidden files" are files with name prefix ., e.g. /home/pxf/.xxx.
.xxx is an invisible file and 'ls' will not list it.
Is there a concept of "hidden file" On Linux Kernel? I mean that are there difference between "regular files" and "hidden files"?
Or just it's a conventional rule that a file with prefix . will not be shown by default such as ls. (except with -a option)?
See Wikipedia: Hidden file and hidden directory
They are not a security mechanism because access is not restricted - usually the intent is simply not "clutter" the display of the contents of a directory listing with files the user did not directly create.
This is just a convenient convention that application may or may not observe. The invisibility of these files is not enforced by the kernel.