Assumptions is an option for functions such as Simplify, Refine, and Integrate that specifies default assumptions to be made about symbolic quantities.
DifferentialD[x] displays as \[DifferentialD]x.
PrincipalValue is an option for Integrate that specifies whether the Cauchy principal value should be found for a definite integral.
Interval[{min, max}] represents the range of values between min and max. Interval[{min_1 , max_1}, {min_2 , max_2}, ...] represents the union of the ranges min_1 to max_1, ...
Throughout Mathematica there is support not only for approximate real numbers, but also for exact numbers represented in algebraic or symbolic form. Functions like Floor, ...
AccumulativeSwingIndex
SwingIndex
Just as normal and stable distributions are natural limit distributions when considering linear combinations such as means of independent variables, extreme value ...
Residue
(Built-in Mathematica Symbol) Residue[expr, {z, z_0}] finds the residue of expr at the point z = z_0.
E
(Built-in Mathematica Symbol) E is the exponential constant E (base of natural logarithms), with numerical value \[TildeEqual] 2.71828.