PlotRegion is an option for graphics functions that specifies what region of the final display area a plot should fill.
PopupView[{expr_1, expr_2, ...}] represents an object which displays as a popup menu whose items are the expr_i.PopupView[{expr_1, expr_2, ...}, i] makes the i\[Null]^th ...
PrivateEvaluationOptions -> {opt_1 -> val_1, opt_2 -> val_2} is an option for selections that specifies settings for evaluation-related suboptions.
Protected is an attribute which prevents any values associated with a symbol from being modified.
Put
(Built-in Mathematica Symbol) expr >> filename writes expr to a file. Put[expr_1, expr_2, ..., " filename"] writes a sequence of expressions expr_i to a file. Put["filename "] creates an empty file with ...
Quit
(Built-in Mathematica Symbol) Quit[] terminates a Mathematica kernel session.
RadicalBox[x, n] is a low-level box construct that represents the displayed object Power[x, (n)^-1] in notebook expressions.
RasterSize is an option for Rasterize and related functions that determines the absolute pixel size of the raster generated.
Residue
(Built-in Mathematica Symbol) Residue[expr, {z, z_0}] finds the residue of expr at the point z = z_0.
RowBox
(Built-in Mathematica Symbol) RowBox[{box_1, box_2, ...}] is a low-level box construct that represents a row of boxes or strings in a notebook expression.