NotebookInformation[] gives a list of properties of the current evaluation notebook.NotebookInformation[notebook] gives a list of properties for the specified notebook.

NotebooksMenu is a global option that specifies which recently opened notebooks are listed under the File menu.

Null is a symbol used to indicate the absence of an expression or a result. It is not displayed in ordinary output. When Null appears as a complete output expression, no ...

OptionInspectorSettings -> {opt_1 -> val_1, opt_2 -> val_2, ...} is a global option that specifies the display of options in the Option Inspector.

Padding is an option to various array and image operations that specifies what padding to use when extending beyond the original data specified.

PassEventsUp is an option to EventHandler that specifies whether events handled by a particular event handler should be passed up to event handlers in outer expressions.

PolynomialQ[expr, var] yields True if expr is a polynomial in var, and yields False otherwise. PolynomialQ[expr, {var_1, ...}] tests whether expr is a polynomial in the var_i.

PositiveDefiniteMatrixQ[m] tests whether m is a positive definite matrix.

PrecedenceForm[expr, prec] prints with expr parenthesized as it would be if it contained an operator with precedence prec.

PreemptProtect[expr] evaluates expr, without any interruption from preemptive evaluations.