Winrunner has default GUI objects like Windows, 
PushButton , Check box etc., these objects are called as 
standard objects. This objects can automatically learn by 
winrunner from our application.
 
Some applications use new objects other than winrunner 
standard objects. Those are called as custom objects. These 
should be mapped to the comparable standard GUI objects by 
using GUI map configuration to identify by winrunner.

To treat bitmap objects as push button(GUI object) , we 
have to define that bitmap as a virtual object by using 
virtual object wizard. Then this bitmap is calles virtual 
push button. Like wise we can create virtual radio button , 
lists , tables etc.

This answer is correct for WR
This Question is For SilkTest.Please tell me the answer for
this question.

Most of the development environments has their built-in set 
of GUI controls, these are called as standard objects. For 
most of the standard controls of supported technologies 
SilkTest has mapped classes. While developing any 
application developer may create a new GUI control these 
controls are called as custom object. As it is a user 
created control SilkTest do not have a mapped class for it, 
therefore these type of controls will be identified as 
Custom window (Custom objects) by SilkTest.