RoundingRadius is an option for Rectangle, Framed, and related functions that specifies the radius of the circle to use in rendering rounded corners.
Rule
(Built-in Mathematica Symbol) lhs -> rhs or lhs -> rhs represents a rule that transforms lhs to rhs.
RuntimeAttributes is an option for Compile that specifies attributes for the compiled function it creates.
Scrollbars is an option for Pane that specifies whether scrollbars should be displayed.
Set
(Built-in Mathematica Symbol) lhs = rhs evaluates rhs and assigns the result to be the value of lhs. From then on, lhs is replaced by rhs whenever it appears. {l_1, l_2, ...} = {r_1, r_2, ...} evaluates ...
ShortDownArrow[x, y, ...] displays as x\[ShortDownArrow]y\[ShortDownArrow]....
ShortLeftArrow[x, y, ...] displays as x \[ShortLeftArrow] y \[ShortLeftArrow] ....
ShortRightArrow[x, y, ...] displays as x \[ShortRightArrow] y \[ShortRightArrow] ....
ShortUpArrow[x, y, ...] displays as x\[ShortUpArrow]y\[ShortUpArrow]....
Show
(Built-in Mathematica Symbol) Show[graphics, options] shows graphics with the specified options added. Show[g_1, g_2, ...] shows several graphics combined.