MakeExpression[boxes, form] is the low-level function used in Mathematica sessions to construct expressions from boxes.
NHoldRest is an attribute which specifies that all but the first argument to a function should not be affected by N.
NumberFieldIntegralBasis[a] gives an integral basis for the field \[DoubleStruckCapitalQ][a] generated by the algebraic number a.
ObservableModelQ[ss] gives True if the StateSpaceModel object ss is observable, and False otherwise.
Polygon
(Built-in Mathematica Symbol) Polygon[{pt_1, pt_2, ...}] is a graphics primitive that represents a filled polygon. Polygon[{{pt_11, pt_12, ...}, {pt_21, ...}, ...}] represents a collection of polygons.
Regularization is an option for Sum and Product that specifies what type of regularization to use.
ScrollingOptions -> {opt_1 -> val_1, opt_2 -> val_2, ...} is an option for notebooks that specifies settings for scrolling.
Short
(Built-in Mathematica Symbol) Short[expr] prints as a short form of expr, less than about one line long. Short[expr, n] prints as a form of expr about n lines long.
Simplify[expr] performs a sequence of algebraic and other transformations on expr, and returns the simplest form it finds. Simplify[expr, assum] does simplification using ...
SplineKnots is an option for B-spline functions and graphics primitives that specifies the positions of knots.