A defered event is an event that is not sent immediately, but at the beginning of the next event loop.

For example, this code:

...
PUBLIC SUB MyTextBox_GotFocus()
  PRINT "GotFocus"
END

PUBLIC SUB MyButton_Click()
  MyTextBox.SetFocus
  PRINT "Click"
END
...

prints the following when you click on the button MyButton:

Click
GotFocus

The MyTextBox_GotFocus event handler is raised after the MyButton_Click has finished, when the next event loop begins.