Containing a number of subdirectory with programs, libraries, documentation, etc.
contains most user commands .
Should not contain binaries necessary for booting the system , which go in /bin. The /bin directory is generally located on the same disk partition as /, which is mounted in read-only mode during the boot process.
/usr/bin/X11 - most often a symbolic link to /usr/X11R6/bin, which contains executable binaries related to the X Window system
/usr/doc - location of miscellaneous documentation, and the main location of program documentation files under Slackware
/usr/include - standard location of include files used in C programs such as stdio.h
/usr/info - primary location of the GNU info system files
/usr/lib - standard library files such as libc.a. Searched by the linker when programs are compiled.
Process is kind of program or task carried out by your PC.
Process defined as: " A process is program (command given by user) to perform specific Job. In Linux when you start process, it gives a number to process (called PID or process-id), PID starts from 0 to 65535. "