SpanCharacterRounding is an option for selections that specifies the method used for rounding a spanning character when its size is to be adjusted.
SpheroidalPS[n, m, \[Gamma], z] gives the angular spheroidal function PS n, m (\[Gamma], z) of the first kind.
StackInhibit[expr] evaluates expr without modifying the evaluation stack.
Streams
(Built-in Mathematica Symbol) Streams[] gives a list of all streams that are currently open. Streams["name"] lists only streams with the specified name.
TraceDepth is an option for Trace and related functions which specifies the maximum nesting of evaluation chains that are to be included.
Weights
(Built-in Mathematica Symbol) Weights is an option for various fitting and other functions which specifies weights to associate with data elements.
WindowElements is a notebook option that specifies the elements to include in the window used to display the notebook on the screen.
WordCharacter represents a letter or digit character in StringExpression.
$ControlActiveSetting is a symbol whose value is True if it is evaluated while a control is active, or in certain other previewing situations.
$Echo
(Built-in Mathematica Symbol) $Echo gives a list of files and pipes to which all input is echoed.