StreamPosition[stream] returns an integer that specifies the position of the current point in an open stream.

Stub is an attribute which specifies that if a symbol is ever used, Needs should automatically be called on the context of the symbol.

Top is a symbol that represents the top for purposes of alignment and positioning.

Visible is a notebook option which specifies whether the notebook should be explicitly displayed on the screen.

WindowFloating is a notebook option that specifies whether the window for the notebook should float on top of other windows when it is displayed on the screen.

WordCharacter represents a letter or digit character in StringExpression.

$Context is a global variable that gives the current context.

$InitialDirectory gives the initial directory when the current Mathematica session was started.

$MachineName is a string that gives the assigned name of the computer on which Mathematica is being run, if such a name is defined.

$UserName gives the login name of the user who invoked the Mathematica kernel, as recorded by the operating system.