What is meant by __('page','twentytwelve')

I’m using twentytwelve theme with 1.0 version. I saw many codes like following,

'name' = __('page','twentytwelve');

If I give,

'name' = 'page';

It’s also working fine. Then why using __()?
What is use of that?

Solutions Collecting From Web of "What is meant by __('page','twentytwelve')"

Internationalization and localization (commonly abbreviated as i18n
and l10n respectively) are terms used to describe the effort to make
WordPress (and other such projects) available in languages other than
English, for people from different locales, who use different dialects
and local preferences.

__() is used when the message is passed as an argument to another function. _e() is used to write the message directly to the page. More detail on this @ http://codex.wordpress.org/Translating_WordPress