file.cdf is a Computable Document Format file.

file.nb is a Mathematica notebook file.

Show Expression toggles between the expression and display forms of a cell.

Stylesheet assigns a stylesheet to the current notebook.

AllowReverseGroupClose is an option for Cell that specifies whether a cell group can be reverse closed.

Bookmarks is an option for Manipulate and related functions that gives a list of bookmark settings.

ButtonFunction is an option for the low-level function ButtonBox that specifies the function to execute when the button is active and is clicked.

DockedCells is an option for notebooks that gives a list of cells that are to be displayed "docked" at the top of the notebook.

Evaluatable is an option for Cell that specifies whether a cell should be used as input to be evaluated by the Mathematica kernel.

Language is a global option that specifies the language in which menus, dialog boxes, error messages, and help files are displayed.