Pedal Line
Mark a point 
on a side of a Triangle and draw the perpendiculars from the point to the two other sides. The linebetween the feet of these two perpendiculars is called the pedal line.
- Dispersion (Statistics)
- Disphenocingulum
- Disphenoid
- Dissection
- Dissection Puzzles
- Dissipative System
- Distance
- Distinct Prime Factors
- Distribution
- Distribution Function
- Distribution (Functional)
- Distribution Parameter
- Distribution (Statistical)
- Distributive
- Distributive Lattice
- Disymmetric
- Ditrigonal Dodecadodecahedron
- Ditrigonal Dodecahedron
- Divergence
- Divergenceless Field
- Divergence Tests
- Divergence Theorem
- Divergent Sequence
- Divergent Series
- Diversity Condition