Usability Testing means checking the user-friendly  of 
application . i.e how much user-friendly that application 
is.in this we take survey also etc.

user friendly means how much the s/w application is easy to
use and understand for users .

In usability testing we test whether the application is 
userfriendly or not .

Testing to determine whether the system/software meets the 
specified usability requirements......
swapnil

user friendliness of screens of the build. during this 
testing testers has to perform below sub tests
 1. user interface testing
          a.  Look & feel
          b.  Ease of use 
          
 2. Manual support test

We will conduct usability testing to know the easy ness and 
user friendly ness of the application/web site.
Types are
Navigational Flow testing
User interfance testing
the primary objective of usability testing is to check the 
navigational flow ie how a web site is navigating as 
specified from one page to other.
whether all the basic functionality is present in all the 
pages or not ie ex., menus like file, edit, view...
according to your application.
User interface tesing means..
spell cheks, fonts, images, resize obtions... are specified 
as per functionality or not