Ol
- Olbers Paradox
- If the Universe is infinite, uniform, and unchanging then the entire sky at night would be bright, about as bright as the Sun.
- Oldham Coupling
- A double slider connection used to connect shafts which have only lateral misalignment.
- Oleoresin
- A natural plant product that contains oil and resins, an example is turpentine.
- Oligocene
- The geological period covering about 35.5 million years ago to 23.5 million years ago.
- Olive Oil
- Obtained from the fruit of Olea Europaea.