$MinPrecision (Built-in Mathematica Symbol)

$MinPrecision gives the minimum number of digits of precision to be allowed in arbitrary-precision numbers.

$ModuleNumber (Built-in Mathematica Symbol)

$ModuleNumber gives the current serial number to be used for local variables that are created.

$NewMessage (Built-in Mathematica Symbol)

$NewMessage is a global variable which, if set, is applied to the symbol name and tag of messages that are requested but have not yet been defined.

$NewSymbol (Built-in Mathematica Symbol)

$NewSymbol is a global variable which, if set, is applied to the name and context of each new symbol that Mathematica creates.

$Notebooks (Built-in Mathematica Symbol)

$Notebooks is True if Mathematica is being used with a notebook-based front end.

$NumberMarks (Built-in Mathematica Symbol)

$NumberMarks gives the default value for the option NumberMarks, which specifies whether ` marks should be included in the input form representations of approximate numbers.

$OperatingSystem (Built-in Mathematica Symbol)

$OperatingSystem is a string giving the type of operating system under which Mathematica is being run.

$Output (Built-in Mathematica Symbol)

$Output gives the list of files and pipes to which standard output from Mathematica is sent.

$OutputSizeLimit (Built-in Mathematica Symbol)

$OutputSizeLimit specifies the maximum size in bytes of expressions that will automatically be output in their entirety in a Mathematica notebook.

$Packages (Built-in Mathematica Symbol)

$Packages gives a list of the contexts corresponding to all packages which have been loaded in your current Mathematica session.