What is a Theme textdomain?

I’ve found that any WordPress theme uses this functions, but I don’t understand what is the purpose of it and what is it, in this case 'themify'?
Here are some examples in Themify functions.php:

1).

load_theme_textdomain( 'themify', TEMPLATEPATH.'/languages' );

2).

if (function_exists('register_nav_menus')) {
        register_nav_menus( array(
            'main-nav' => __( 'Main Navigation', 'themify' ),
            'footer-nav' => __( 'Footer Navigation', 'themify' ),
        ) );
    }

And in tempate file:

3). <?php _e( 'Sorry, nothing found.', 'themify' ); ?>

And many more! My doubt is what is 'themify' stand for? What is their purpose? Could I Change it or delete it? What is the place, 'themify', for?

Answers:

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Method 1

In this case, 'themify' is the defined textdomain for the Theme, used to make the Theme translatable. (Codex reference: load_theme_textdomain()).

Making a Theme translation-ready requires a few steps.

1. Define the Theme’s textdomain:

   load_theme_textdomain( 'themify', TEMPLATEPATH.'/languages' );

2. Define translatable strings in the template.

   This is done using one of a few translation functions: __() (for returned strings), _e() (for echoed strings), and _x()/_ex() (for gettext context strings). There are others, but you get the idea…

   A static text string, such as <p>Hello world!</p>, is wrapped in an appropriate translation function, such as <p><?php _e( 'Hello World!', 'themify' ); ?></p>, to make it available for translation.

3. Generate the .mo/.po files
   _{reference on how to edit language files}

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