Dedekind Cut
A set partition of the Rational Numbers into two nonempty subsets 
and 
such that allmembers of are less than those of and such that has no greatest member. Real Numbers can be defined using either Dedekind cuts or Cauchy Sequences.
References
Courant, R. and Robbins, H. ``Alternative Methods of Defining Irrational Numbers. Dedekind Cuts.'' §2.2.6 in What is Mathematics?: An Elementary Approach to Ideas and Methods, 2nd ed. Oxford, England: Oxford University Press, pp. 71-72, 1996.
- Spherical Bessel Differential Equation
- Spherical Bessel Function
- Spherical Bessel Function of the First Kind
- Spherical Bessel Function of the Second Kind
- Spherical Bessel Function of the Third Kind
- Spherical Cap
- Spherical Coordinates
- Spherical Design
- Spherical Excess
- Spherical Frustum
- Spherical Geometry
- Spherical Hankel Function of the First Kind
- Spherical Hankel Function of the Second Kind
- Spherical Harmonic
- Spherical Harmonic Addition Theorem
- Spherical Harmonic Closure Relations
- Spherical Harmonic Tensor
- Spherical Helix
- Spherical Point System
- Spherical Polygon
- Spherical Ring
- Spherical Sector
- Spherical Segment
- Spherical Shell
- Spherical Spiral