theme_text_domain what is it and what does it want?

Im adding a sidebar and I see the name field of the array says twentytwelve. I understand that is called the “theme_text_domain” but the page does not explain that it is or what it means or why its there. looks like its simply supposed to be the theme name. Is it? not very intuitive or semantic.

Can someone shed some light on this, as I find little info.
thanks

Norman

register_sidebar( array(
		'name' => __( 'Main Sidebar', 'twentytwelve' ),
		'id' => 'sidebar-1',
		'description' => __( 'Appears on posts and pages except the optional Front Page template, which has its own widgets', 'twentytwelve' ),
		'before_widget' => '<aside id="%1$s" class="widget %2$s">',
		'after_widget' => '</aside>',
		'before_title' => '<h3 class="widget-title">',
		'after_title' => '</h3>',
	) );