Underlined represents an underlined font.
UnsavedVariables is an option for Manipulate, DynamicModule, and related functions that specifies local symbols that should not be saved when the notebook containing them is ...
VectorColorFunction is an option for VectorPlot and related functions which specifies a function to apply to determine colors of field vectors drawn.
WindowFrameElements is an option for notebooks that specifies the elements to include in the frame of the window used to display the notebook on the screen.
WordSearch is an option for Find and FindList that specifies whether the text searched for must appear as a word.
$Aborted is a special symbol that is returned as the result from a calculation that has been aborted.
$CommandLine is a list of strings giving the elements of the original operating system command line with which Mathematica was invoked.
$Display gives a list of files and pipes to be used with the default $DisplayFunction.
$MachinePrecision gives the number of decimal digits of precision used for machine-precision numbers.
$MachineType is a string giving the general type of computer on which Mathematica is being run.