Context module allows you to manage contextual conditions and reactions for different portions of your site. You can think of each context as representing a "section" of your site. For each context, you can choose the conditions that trigger this context to be active and choose different aspects of Drupal that should react to this active context.
Context UI :-
Context UI provides an administrative interface for managing and editing Contexts. It is not necessary for the proper functioning of contexts once they are built and can be turned off on most production sites.
Context layouts :-
Context Layouts provides a formalized way for themes to declare and switch between page templates using Context. It is a continuation of an old Drupal themer's trick to switch to something besides the standard page.tpl.php file for a variety of special case pages like the site frontpage, login page, admin section, etc.
Reference:- http://drupal.org/project/context