SELinux

Question 1

define Subject

Answer 1

any user or process that access an object
system_u for SELinux system user
unconfined_u for subjects that are not bound by SELinux policy

Question 2

define Object

Answer 2

a resource such as a file, directory, hardware device, network interface, port, pipe, or socket, that a subject accesses
object_r - general objects
system_r - system own objects
unconfined_r - not bound by SELinux