ZeroWidthTimes is an option for selections that specifies whether blank spaces representing multiplication are explicitly shown.
$Aborted is a special symbol that is returned as the result from a calculation that has been aborted.
$AssertFunction specifies a function to apply to assertions that fail.
$CommandLine is a list of strings giving the elements of the original operating system command line with which Mathematica was invoked.
$Context is a global variable that gives the current context.
$CreationDate gives the date and time at which the particular release of the Mathematica kernel you are running was created.
$DisplayFunction gives the default setting for the option DisplayFunction in graphics functions.
$Display gives a list of files and pipes to be used with the default $DisplayFunction.
$DynamicEvaluation is a symbol whose value is True if it is evaluated as part of the evaluation of a Dynamic.
$Epilog
(Built-in Mathematica Symbol) $Epilog is a symbol whose value, if any, is evaluated when a dialog or a Mathematica session is terminated.