Formulas
- Optical fiber
- Optical metric
- Optimal instruments
- Optional stopping theorem
- Orbital eccentricity
- Orbital elements
- Order statistic
- Orders of magnitude (length)
- Ordinal date
- Ordinal regression
- Ordinary least squares
- Original proof of Gödel's completeness theorem
- Orthogonal convex hull
- Orthogonal matrix
- Orthoptic (geometry)