Virtual Keys
A virtual key is the key that is actually pressed on the keyboard.  The VK value for a letter, say 'a' is the same for lower case 'a' and upper case 'A' because it refers to the key pressed on the keyboard, not to the ASCII value of the input.  Most keys have a graphical representation.  Pressing the 'a' key in a text window causes the letter 'a' to be displayed in the window.  There are some keys that do not have a graphical representation.  It is necessary to use Virtual Key Codes to discover which of these keys has been pressed.  They include the arrow keys, the F-keys, Shift, Ctrl, Alt, Del, etc.

Some other virtual key code constants:
  F1 through F16 		_VK_F1 through _VK_F16
  0 through 9 on regular keyboard _VK_0 through _VK_9
  0 through 9 on number pad	_VK_NUMPAD0 through _VK_NUMPAD9
  a through z 			_VK_A through _VK_Z
  Alt				_VK_MENU
  Shift				_VK_SHIFT
  Home				_VK_HOME
  End				_VK_END
  Insert				_VK_INSERT
  Delete				_VK_DELETE
  NumLock			_VK_NUMLOCK
  Arrow Up			_VK_UP
  Arrow Down			_VK_DOWN
  Arrow Left			_VK_LEFT
  Arrow Right			_VK_RIGHT