The terminal is an interface in which you can type and execute text based commands.Basically it is a "CLI" command line interface You can see it in the image .

                                               Why use it:

It can be much faster to complete some tasks using a Terminal than with graphical applications and menus. Another benefit is allowing access to many more commands and scripts.

A common terminal task of installing an application can be achieved within a single command, compared to navigating through the Software Centre or Synaptic Manager.

For example the following would install Deluge bittorrent client:

sudo apt-get install deluge

To save a detailed list of files in the current directory tree to a file called listing.txt:

find -type f > listing.txt

       Sometimes you will also see the following notation:

 

              $ whoami calum $ ls Downloads Documents

This means that the command whoami is executed which gives calum as output. Following that command, ls is executed which outputs Downloads Documents.

                   

                     A similar notation is:

 

# apt-get update

This means that the command should be run as root, that is,                            using sudo:

$ sudo apt-get update

Note that the # character is also used for comments.

# this command will give your username whoami # the next command will show the contents of the current directory ls

                                         

                                             How do I open a terminal:

• Open the Dash (Super Key) or Applications and type terminal

   

• Use the keyboard shortcut by pressing Ctrl+Alt+T.

• For older or Ubuntu versions: 

  Applications → Accessories → Terminal

                                       

                                          Alternative names for the terminal:

• Console

• Shell

• Command Line

• Command Prompt