NullRecords is an option for Read and related functions which specifies whether null records should be taken to exist between repeated record separators.
NumberMultiplier is an option for NumberForm and related functions which gives the string to use as a multiplication sign in scientific notation.
NumberPoint is an option for NumberForm and related functions which gives the string to use as a decimal point.
Order
(Built-in Mathematica Symbol) Order[expr_1, expr_2] gives 1 if expr_1 is before expr_2 in canonical order, and -1 if expr_1 is after expr_2 in canonical order. It gives 0 if expr_1 is identical to expr_2.
PassEventsDown is an option to EventHandler which specifies whether events handled by a particular event handler should be passed down to event handlers nested inside.
PatternSequence[p_1, p_2, ...] is a pattern object which represents a sequence of arguments matching p_1, p_2, ....
PrintingStyleEnvironment is an option for notebooks which specifies the style environment to be used in printing the notebook on paper.
TraceDepth is an option for Trace and related functions which specifies the maximum nesting of evaluation chains that are to be included.
Visible
(Built-in Mathematica Symbol) Visible is a notebook option which specifies whether the notebook should be explicitly displayed on the screen.
WordCharacter represents a letter or digit character in StringExpression.