NumberMarks is an option for InputForm and related functions that specifies whether ` marks should be included in the printed forms of approximate numbers.

NumberSigns is an option for NumberForm and related functions which gives strings to use as signs for negative and positive numbers.

OddQ[expr] gives True if expr is an odd integer, and False otherwise.

Off[symbol::tag] switches off a message, so that it is no longer printed. Off["name"] switches off a named group of messages.Off[s] switches off tracing messages associated ...

OneIdentity is an attribute that can be assigned to a symbol f to indicate that f[x], f[f[x]], etc. are all equivalent to x for the purpose of pattern matching.

Operate[p, f[x, y]] gives p[f][x, y]. Operate[p, expr, n] applies p at level n in the head of expr.

p : v is a pattern object that represents an expression of the form p, which, if omitted, should be replaced by v.

% n or Out[n] is a global object that is assigned to be the value produced on the n\[Null]^th output line. % gives the last result generated. %% gives the result before last. ...

PackingMethod is an option for GraphPlot and related functions which specifies how disconnected components should be packed together in the layout produced.

ParagraphIndent is an option for Cell which specifies how far in printer's points to indent the first line of each paragraph of text.