ManhattanDistance[u, v] gives the Manhattan or "city block" distance between vectors u and v.
MaxIterations is an option that specifies the maximum number of iterations that should be tried in various built-in functions and algorithms.
MeshShading is an option for plotting functions that gives lists of colors to use for regions between mesh divisions.
NHoldFirst is an attribute which specifies that the first argument to a function should not be affected by N.
NoncentralChiSquareDistribution[\[Nu], \[Lambda]] represents a noncentral \[Chi]^2 distribution with \[Nu] degrees of freedom and noncentrality parameter \[Lambda].
NumberFieldIntegralBasis[a] gives an integral basis for the field \[DoubleStruckCapitalQ][a] generated by the algebraic number a.
Opener
(Built-in Mathematica Symbol) Opener[x] represents an opener with setting x, displayed as OpenerBox[True] when x is True and OpenerBox[False] when x is False. Opener[Dynamic[x]] takes the setting to be ...
OpenWrite["file"] opens a file to write output to it, and returns an OutputStream object. OpenWrite[] opens a new file in the default area for temporary files on your ...
ParallelProduct[expr, {i, i_max}] evaluates the product \[Product]i = 1 i_max expr in parallel.ParallelProduct[expr, {i, i_min, i_max}] starts with i = ...
Pi
(Built-in Mathematica Symbol) Pi is \[Pi], with numerical value \[TildeEqual] 3.14159.