Technology Glossary

Two-Dimensional Material

A material whose functional layer is only one or a few atoms thick.

Two-Factor Authentication(2FA)

An account-security method that requires two different forms of verification, such as a password and a one-time code, before granting access.

Two-Person Cockpit Rule

An operational policy requiring at least two authorized people to remain on the flight deck during specified phases or whenever one pilot leaves.

Two-Stage Classifier

A detection pipeline in which an initial classifier screens inputs or outputs and a second classifier performs a more selective assessment before an action is allowed or blocked.

Ultra-Diffuse Galaxy

An unusually faint class of galaxy that emits very little light for its size, often thought to contain an unusually high proportion of dark matter.

Ultrafast X-Ray Diffraction(UXRD)

A pump-and-probe measurement technique that uses very short X-ray pulses to follow rapid changes in a material's crystal structure. Researchers can infer strain, phase changes and heat movement by tracking how the material's diffraction pattern evolves after excitation.

Umbra

The fully dark, cone-shaped inner part of a shadow. When the Moon's umbra reaches Earth's surface, observers inside it see a total solar eclipse.

Uniform Guidance

The US government-wide framework for administering federal grants and other financial assistance. It sets common requirements for areas such as costs, audits, procurement, oversight and recipient responsibilities. Agencies apply the framework alongside program-specific laws and conditions, so it creates a shared baseline rather than one identical grant contract.

Unit-Distance Graph

A graph whose vertices can be placed as distinct points in the Euclidean plane so that every connected pair is exactly one unit apart. Pairs at unit distance do not always have to be connected, depending on whether the graph is defined as a subgraph of the full unit-distance graph.

Unlawful Interference

An act or attempted act that endangers civil aviation security, including seizure of an aircraft, violence on board, sabotage, or unauthorised intrusion into protected aviation areas.

Unmanned Ground Vehicle(UGV)

A vehicle that moves on land without a person on board. It may be remotely operated, follow programmed routes or use sensors and software for varying levels of autonomous movement.

Upper Troposphere

The higher part of the lowest atmospheric layer, where large-scale winds and cloud structures can be observed.

Uranium-Thorium Dating(U-Th)

A radiometric dating method that measures uranium decay products to determine the age of calcium carbonate materials such as coral.

Urban Canyon

An urban canyon is a street or built-up area surrounded by tall buildings that block and reflect satellite signals. GNSS receivers in these environments may see fewer satellites and suffer multipath errors, reducing positioning accuracy.

Utility Factor

For plug-in hybrid vehicles, the estimated share of total driving completed using electricity rather than fuel. It is derived from assumptions or real-world data about trip distances, charging frequency, battery range, and driver behavior.

Utility-Scale Quantum Computer

A quantum computer whose computational value exceeds the full cost of building and operating it for at least some real tasks. The concept requires useful performance, reliability and economics, not merely a high physical-qubit count.

Vaccine Immunogenicity

The ability of a vaccine to trigger measurable immune responses, such as antibodies or immune-cell activity. Immunogenicity is evidence of an immune reaction, but it does not by itself prove protection against infection or severe disease.

Vacuum Birefringence

A quantum-electrodynamic effect in which an extremely strong magnetic or electric field makes empty space alter light differently according to its polarization. The predicted change is tiny under terrestrial conditions but can become measurable around magnetars.

Vagus Nerve Stimulation(VNS)

A therapy that delivers controlled electrical pulses to the vagus nerve, usually through an implanted electrode, to influence connected neural circuits. It is used for selected conditions such as epilepsy and treatment-resistant depression, with benefits and risks depending on the indication and device programming.

Valve-Engineered Tissue

A laboratory-built tissue designed to reproduce important cellular, structural and mechanical features of a heart valve. Researchers use it to study valve biology, test treatments or investigate future replacement materials.

Van der Waals Force

A weak attraction between nearby atoms or molecules caused by temporary or permanent distributions of electric charge. Although small for a single pair, the combined attraction across a surface can hold nanoscale layers or components together.

Viral Replication

The process by which a virus uses host-cell machinery to copy its genetic material and produce new viral particles.

Viral Reservoir

A pool of long-lived cells in the body that harbor a dormant virus, letting it persist and later reactivate even when no active infection is detectable in the blood.

Virtual Asset Service Provider(VASP)

A business that exchanges, transfers, safeguards or administers cryptocurrencies and other virtual assets for customers. Depending on the country, it may need a licence and must follow rules on identity checks, fraud prevention, record keeping and suspicious transactions.

Virtual Unwrapping

A computational technique for reading rolled, folded, or sealed documents without physically opening them. Three-dimensional scans are segmented to identify surfaces, digitally flatten them, and reveal writing using differences in material or imaging signals.

Technology glossary