UnderscriptBox (Built-in Mathematica Symbol)

UnderscriptBox[x, y] is the low-level box representation for UnderscriptBox[x, y] in notebook expressions.

Uninstall (Built-in Mathematica Symbol)

Uninstall[link] terminates an external program started by Install, and removes Mathematica definitions set up by it.

ValueQ (Built-in Mathematica Symbol)

ValueQ[expr] gives True if a value has been defined for expr, and gives False otherwise.

$BatchInput (Built-in Mathematica Symbol)

$BatchInput is True if input in the current session is being fed directly to the Mathematica kernel in batch mode.

$LicenseID (Built-in Mathematica Symbol)

$LicenseID is a string that gives the license ID under which Mathematica is being run.

$MaxPrecision (Built-in Mathematica Symbol)

$MaxPrecision gives the maximum number of digits of precision to be allowed in arbitrary-precision numbers.

$ProcessorCount (Built-in Mathematica Symbol)

$ProcessorCount gives the number of processor cores available on the computer system on which Mathematica is being run.

$RootDirectory (Built-in Mathematica Symbol)

$RootDirectory gives the root directory of your file system.

$TimedOut (Built-in Mathematica Symbol)

$TimedOut is a special symbol returned by certain functions when an operation times out.

Executing Notebook Commands Directly in ... (Mathematica Tutorial)

When you execute a command like NotebookWrite[obj,data] the actual operation of inserting data into your notebook is performed in the front end. Normally, however, the kernel ...