- one-to-one relation
- one-to-one representation
- one-unit maintainable system
- one-valued
- one-valued branch
- one-valued function
- one-valued mapping
- one-variable calculus
- one-way channel
- one-way classification
- one-way function
- one-way hash function
- one-way infinite Turing machine
- one-way layout
- one-way trapdoor function
- online analysis
- online (= on-line)
- online system
- on-off element
- Ono inequality
- Ono Takash
- O-notation
- Onsager differential equation
- Onsager, L.
- Onsager reciprocity relation