form field "std" => __(

Hi,

i’m trying to understand some of theme options pages as plugins options.
in several cases i can find options stored as:

"id" => "blog_small_text",
"std" => __('hello world', 'wp-test'),

please could you redirect me or tell me what is the purpose of ‘wp-test’ in “std” variable ?

as far i as understood it’s a textdomain variable, but what does it mean ?
in case we want to translate the “blog_small_text” variable in several languages, should we include in wmpl-config.xml the ‘wp-test’ ?

thx