Eulerian Circuit
An Eulerian Trail which starts and ends at the same Vertex. In other words, it is a Cycle which uses each Edge exactly once. The term Eulerian Cycle is also used synonymously with Euleriancircuit. For technical reasons, Eulerian circuits are easier to study mathematically than are HamiltonianCircuits. As a generalization of the Euler 
showed (without proof) that a Connected Graph has an Eulerian circuit Iff it hasno Vertices of Odd Degree.
- Oblate Spheroidal Coordinates
- Oblate Spheroidal Wave Function
- Oblate Spheroid Geodesic
- Oblique Angle
- Oblong Number
- Obstruction
- Obtuse Angle
- Obtuse Triangle
- Ochoa Curve
- Octacontagon
- Octadecagon
- Octagon
- Octagonal Number
- Octagram
- Octahedral Graph
- Octahedral Group
- Octahedral Number
- Octahedron
- Octahedron 5-Compound
- Octahemioctacron
- Octahemioctahedron
- Octakaidecagon
- Octal
- Octant
- Octatetrahedron