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HE-AAC
HE-AAC, also known as aacPlus, is an audio coding profile that extends AAC with Spectral Band Replication, standardized in 2003 and used in DAB+ digital radio.
Head gasket
A head gasket, also called a cylinder head gasket, is the seal between the cylinder head and engine block, keeping combustion pressure, oil, and coolant separate.
Head restraint
A head restraint is a pad on a vehicle seat or the top of the seat back that limits rearward head movement and reduces whiplash injury in rear collisions.
Head-driven phrase structure grammar
Head-driven phrase structure grammar (HPSG) is a lexicalist, unification-based theory of syntax introduced by Carl Pollard and Ivan Sag in 1987, where most grammatical information is carried by lexical entries.
Head-of-line blocking
Head-of-line (HOL) blocking is a performance problem where the first item in a FIFO queue blocks items behind it, notably in packet switches and TCP.
Head-up display
A head-up display (HUD), also called a head-up guidance system, projects flight information onto a transparent screen in the pilot's forward view, originating in military aviation.
Headbox
The headbox, also called a flow box, is the device at the wet end of a paper machine that spreads pulp as a uniform thin jet onto the forming wire.
Headhouse
A headhouse is the portion of a railway terminal without tracks and platforms, holding ticket counters, waiting rooms, and baggage facilities; the term also covers subway and ventilation structures.
Headlamp
A headlamp is a lamp mounted on the front of a motor vehicle to light the road at night, with lower beams for close range and upper beams for distance.
Headless data architecture
Headless data architecture decouples data ownership, business rules, and APIs from the applications that consume them, using a shared stream (Kafka) and table (Iceberg) layer with pluggable processing heads; distinct from headless CMS and data lakes.
Headless UI
Headless UI is a set of unstyled, fully accessible UI components for React and Vue, created by Tailwind Labs to pair with Tailwind CSS, with version 1.0 released in 2021.
Headrace and tailrace tunnels
Headrace and tailrace tunnels are hydropower tunnels conveying water from an intake to an underground powerhouse and back to the river, built as pressurized or free-flow tunnels.
Heads of state and government killed in aviation accidents
The list of heads of state and government killed in aviation accidents covers presidents, prime ministers, and monarchs who died in crashes from 1936 to 2024.
Headspace (company)
Headspace, also known as Headspace Health, is an American digital mental health company founded in 2010 by Andy Puddicombe and Richard Pierson, best known for its meditation app.
Headway (transport)
In transport, headway is the time or distance separating consecutive vehicles running on the same line in the same direction, central to railway capacity planning.
Health Catalyst, Inc.
Health Catalyst, Inc. is an American healthcare data and analytics company founded in 2008 and headquartered in South Jordan, Utah, trading on Nasdaq under the ticker HCAT.
Health Connect
Health Connect is an on-device Android health data platform, announced by Google in 2022, that lets health and fitness apps share data through a single set of APIs.
Health Gorilla, Inc.
Health Gorilla is an American healthcare interoperability company in Coral Gables, Florida, operating a clinical data exchange network and designated a QHIN under TEFCA in December 2023.
Health informatics
Health informatics, also called medical or clinical informatics, is the interdisciplinary field applying computer and information science to health data, aiming to improve human health and care delivery.
Health Level 7
Health Level 7, also known as Health Level Seven, is a not-for-profit standards organization founded in 1987, best known for its Version 2 messaging standard and the FHIR framework for exchanging electronic health information.
Health threat from cosmic rays
The health threat from cosmic rays is the risk space radiation poses to astronauts outside Earth's protective magnetic field, including cancer, nervous system damage, and cataracts.
HealthBench
HealthBench is an open medical benchmark released by OpenAI in May 2025, measuring how language models handle realistic health conversations graded against rubrics written by 262 physicians.
Healy device
The Healy is a palm-sized wearable microcurrent device sold by Healy World, a German direct-selling company, and cleared by the FDA in 2019 for temporary pain relief.
Heap (data structure)
A heap is a tree-based data structure satisfying the heap property, so the smallest or largest element sits at the root; the binary heap underlies priority queues and heapsort.
Heap leaching
Heap leaching is a hydrometallurgical extraction method in which crushed ore is stacked on a lined pad and irrigated with a solution that dissolves the metal.
Heapsort
Heapsort is a comparison-based sorting algorithm that arranges the input as a binary heap and repeatedly extracts the largest element, sorting in place in O(n log n) worst-case time.
HEARO
HEARO is a task-autonomous surgical robot for cochlear implantation developed at the University of Bern and commercialized by CAScination and MED-EL, receiving its CE mark in 2020.
Hearse
A hearse, also called a funeral coach, is a vehicle built to carry a coffin at a funeral, typically leading the procession from service to burial.
Hearst Castle
Hearst Castle, formally La Cuesta Encantada, is a hilltop estate at San Simeon on California's Central Coast, built for publisher William Randolph Hearst by architect Julia Morgan between 1919 and 1947.
Heart Aerospace
Heart Aerospace is an electric aircraft manufacturer founded in 2018 in Gothenburg, Sweden, that develops hybrid-electric regional airliners, including the 30-seat ES-30 and the 36-seat ES-36 unveiled in 2026.