Technology glossary

On-to-Off Current Ratio

The ratio between a transistor's current when fully on and its leakage current when off. A high ratio helps circuits distinguish logic states while limiting unwanted power loss.

Open-Weight Model

An AI model whose trained numerical parameters, or weights, are made available for others to download and run. Open weights do not necessarily mean that the training data, source code, or full development process is publicly disclosed or unrestricted.

Operational Design Domain(ODD)

The specific roads, weather, speeds and other conditions in which an automated driving system is designed to operate.

Operational Lifetime

The period during which a device, component, or system continues to perform within specified limits under stated operating conditions. It may end because of wear, material degradation, performance loss, or failure, and can differ from shelf life.

Operational Technology(OT)

Hardware and software that monitor or control physical equipment and industrial processes, such as pumps, valves and treatment systems.

Operational Weather Model

A forecasting model run routinely on a fixed schedule with real-time observations and quality controls to support official weather services and decisions.

Optical Player Tracking

A camera-based system that estimates player and ball positions continuously during a match.

Optomechanical Surface

A surface whose visible optical behavior changes through controlled mechanical movement. It combines structures that guide light with parts that slide, rotate or deform to select a visual state.

Orbital Insertion

The maneuver that gives a spacecraft enough horizontal velocity to enter its intended orbit rather than falling back to Earth. Reaching space above a chosen altitude is not sufficient unless the vehicle also achieves the required speed and direction.

Orbital Launch Vehicle

A rocket-powered vehicle designed to carry a payload from Earth into orbit. It may use one or more stages that separate during flight to reduce mass and reach the speed and altitude required for orbit.

Orbital Propagation

The mathematical calculation of an object's future or past position from observations of its orbit. Accurate propagation must account for gravity, solar radiation pressure and measurement uncertainty, especially for distant or tumbling objects.

Orbital Reflector

An object placed in orbit and designed to reflect sunlight toward Earth or another target. Proposed uses include illumination, signaling, and experiments, but large or bright reflectors may create space-debris, astronomical-observation, environmental, and governance concerns.

Out-of-Distribution Generalization(OOD generalization)

A model's ability to perform reliably on data that differs meaningfully from the distribution represented in its training set. It tests whether the model learned transferable patterns rather than relying only on correlations specific to familiar conditions.

Outer Radial Glia

A subtype of radial glial progenitor abundant in the developing human cortex. Its capacity for repeated division is associated with expansion and folding of the cerebral cortex.

Over-the-Air Update(OTA)

Software delivered wirelessly to a connected vehicle or device without a workshop visit. It can change control behavior and add safety responses, but it cannot replace a physical component when the hardware itself needs redesign.

Overall Survival(OS)

The time from a defined starting point, such as randomization or treatment initiation, until death from any cause. It is a direct clinical-trial endpoint, although results can take a long time to mature and may be influenced by treatments received after the study intervention.

Oxidative Hydrothermal Dissolution

A treatment that uses water and oxygen at elevated temperature and pressure to break resistant organic materials into smaller molecules that microbes or chemical processes can use.

Oxygen Evolution Reaction(OER)

The electrochemical step in which oxygen atoms combine and are released as gas at an electrode, the reaction that occurs when a solid oxide or electrolysis cell splits water to produce hydrogen.

Oxygen Reduction Reaction(ORR)

The electrochemical step in which oxygen gains electrons at an electrode, the reaction that generates electricity in a fuel cell or solid oxide cell.

Oxytocin

A hormone and neurotransmitter, sometimes called the 'bonding hormone,' that rises during trust-building social contact such as physical touch, cooperation and close relationships, and is increasingly studied for its role in signaling vigilance as well as connection during social interactions.

Paleoclimate Proxy

A natural archive such as coral, ice or sediment whose physical or chemical properties are used to estimate past climate conditions.

Pancreatic Ductal Adenocarcinoma(PDAC)

The most common form of pancreatic cancer, arising from cells that line the pancreatic ducts. It is often diagnosed after it has spread and is biologically distinct from pancreatic neuroendocrine tumours.

Paraspeckle

A membraneless structure inside the cell nucleus that organizes specific RNA molecules and proteins.

Passive State Indicator

A visual or physical indicator that communicates the current state of an object without electrical power, often by coupling its display directly to a mechanical position, temperature or material change.

Path of Totality

The narrow track on Earth's surface, typically 100 to 200 kilometers wide, that the Moon's umbra crosses during a total solar eclipse. Only observers inside this path see full darkness.

Payload Fairing

A protective shell around satellites or other payloads at the top of a launch vehicle. It shields them from airflow, heating and contamination during ascent, then separates after the atmosphere becomes thin enough.

PCSK9 Inhibitor

A medicine that blocks the activity of the PCSK9 protein, allowing the liver to remove more LDL cholesterol from the blood. Available approaches include antibodies and gene-silencing drugs; they are generally used for selected patients alongside lifestyle changes and other lipid-lowering treatment.

Peak Warming

The highest level of long-term global temperature increase reached before warming stabilizes or begins to decline. It depends on cumulative greenhouse-gas emissions and how quickly the world reaches net zero.

Peer List Poisoning

The deliberate insertion of false or defender-controlled entries into the list of peers a decentralized application trusts, redirecting or isolating its communications.

Peer Review

A process in which qualified experts evaluate research proposals, methods, evidence or manuscripts before funding or publication. In grantmaking, reviewers assess factors such as scientific merit, feasibility and potential impact, then provide recommendations to the funding agency. Peer review improves expert scrutiny but does not remove judgment, bias or uncertainty.