Introtext or intro text is a text supports HTML and shortcode to give a space for descriptions before the widget content. Similiar to Outrotext or outro text is a space for descriptions after the widget content.

'intro_text' 	=> $instance['intro_text'],
'outro_text' 	=> $instance['outro_text'],

That’s it, all of our WordPress plugins use the intro and outro text.

The intro and outro text is used per widget instance, every widget have these features. You can see the widget that have an intro and outro text features below:
Extended Tags Widget – WordPress Premium Plugin (Widgets)
Advanced Links Widget – WordPress Premium Plugin
Advanced Categories Widget
Custom Post Widget – WordPress Premium Plugin
Authors Widget – WordPress Premium Plugin (Widgets)
deviantART Widget – WordPress Premium Plugin
zTwitter – Twitter Feed Widget For WordPress