- Objective Function
- Observational Adequacy
- Observations Sequence
- Offline
- On-Line
- Online
- Ontological
- Ontology
- Open Source
- Operations Research
- Optical Character Recognition-OCR
- Optical Spectrometer
- Optimum Situation
- Orthographic
- Orthographic Normalization
- Orthography
- Output
- Output Distributions
- Output Layer
- Over-Segmentation