Abscissa
The 
- (horizontal) coordinate of a point in a two dimensional coordinate system. Physicists and astronomers sometimesuse the term to refer to the axis itself instead of the distance along it.
- Dedekind Function
- Dedekind Ring
- Dedekind's Axiom
- Dedekind's Problem
- Dedekind Sum
- Deducible
- Deep Theorem
- Defective Matrix
- Defective Number
- Deficiency
- Deficient Number
- Definable Set
- Defined
- Definite Integral
- Degenerate
- Degree
- Degree (Algebraic Surface)
- Degree (Map)
- Degree of Freedom
- Degree (Polynomial)
- Degree Sequence
- Degree (Vertex)
- Dehn Invariant
- Dehn's Lemma
- Dehn Surgery