SystemDialogInput["type"] brings up an interactive system dialog and returns the value chosen in the dialog. SystemDialogInput["type", init] uses init as the initial setting ...
SystemInformation[] gives detailed information about the Mathematica system being run. SystemInformation["comp"] gives a list of rules with information about the component " ...
TableHeadings is an option for TableForm and MatrixForm which gives the labels to be printed for entries in each dimension of a table or matrix.
TagBox
(Built-in Mathematica Symbol) TagBox[boxes, tag] is a low-level box construct that displays as boxes but maintains tag to guide the interpretation of boxes on input.
TaggingRules is an option for selections that specifies a list of strings to be associated with a selection.
TextAlignment is an option for Cell, Style and related constructs which specifies how successive lines of text should be aligned.
TextCell["string"] gives a text cell that can appear in a Mathematica notebook.TextCell["string", " style"] gives a text cell with the specified style.
TextJustification is an option for Cell and Inset which specifies how much lines of text can be stretched in order to make them be the same length.
TextRecognize[image] recognizes text in image and returns it as a string.
TextureCoordinateFunction is an option to Plot3D and similar functions that specifies a function that computes texture coordinates.