All articles starting with H

Hyperfocal distance

Hyperfocal distance is the focus distance at which a lens's depth of field extends from half that distance to infinity, widely used in landscape, street, and documentary photography.

Hyperfocus

Hyperfocus: intense, prolonged absorption in one task with diminished awareness of surroundings, reported mainly in ADHD, autism, and schizophrenia; distinct from flow and not a DSM-5 ADHD symptom.

Hyperfunction of pituitary gland

Hyperfunction of pituitary gland (ICD-11 5A60): excessive pituitary hormone production, mostly from hormone-secreting pituitary adenomas, causing acromegaly, gigantism, hyperprolactinaemia, and related syndromes treated by surgery, drugs, and radiation.

Hypergamy

Hypergamy is marrying a person of higher caste, status, education, or income; hypogamy is marrying down. Educational hypergamy (wife less educated) has declined worldwide as women's college attainment reversed the gender gap, making hypogamy now more common in most European countries and rising in the United States.

Hypergeometric distribution

The hypergeometric distribution is a discrete probability distribution counting successes in a random sample drawn without replacement from a finite population, used in acceptance sampling and Fisher's exact test.

Hypergeometric function

The hypergeometric function, also known as the Gauss hypergeometric function or ₂F₁, is a special function defined by a power series that solves a broad class of differential equations.

Hypergeometric series

A hypergeometric series is a power series in which the ratio of consecutive coefficients is a rational function of the index, named by Euler in 1769 and made rigorous by Gauss in 1812.

Hypergiant

A hypergiant is an extremely luminous, massive star showing very high mass loss through stellar winds, classed 0 or Ia+ and lacking an official definition.

Hyperglycemia

Hyperglycemia, or high blood sugar, is an abnormally high concentration of glucose in the blood that defines diabetes mellitus and, when severe, can cause diabetic ketoacidosis.

Hyperglycemic hormone

Crustacean hyperglycemic hormone (CHH), also called hyperglycemic hormone, is a 72-78 amino acid eyestalk neuropeptide of decapod crustaceans that raises hemolymph glucose; it names the CHH family including MIH, VIH, MOIH, and insect ITPs.

Hypergolic propellant

A hypergolic propellant, also called hypergolic fuel, is a rocket propellant combination whose fuel and oxidizer ignite spontaneously on contact, typically monomethylhydrazine and dinitrogen tetroxide, making engines reliable and storable for years in spacecraft.

Hypergonadotropic hypogonadism-cataract syndrome

Hypergonadotropic hypogonadism-cataract syndrome (Lubinsky syndrome, ORPHA:2410, OMIM 240950) is an extremely rare autosomal recessive endocrine disease combining adolescent-onset cataracts with primary gonadal failure; only about three cases are recorded worldwide.

Hypergraph

A hypergraph is a generalization of a graph in which an edge may join any number of vertices rather than exactly two; an ordinary graph is a 2-uniform case.

Sep 29, 2026

Hypergraph convolutional network

A hypergraph convolutional network (HGNN) is a neural network that generalizes graph convolution to hyperedges linking many vertices, introduced by Yifan Feng in 2018 and published at AAAI 2019.

Sep 29, 2026

Hypergraph learning

Hypergraph learning is machine learning on hypergraphs, whose hyperedges connect any number of nodes to model higher-order interactions like co-authorship, with deep-learning methods now predominant.

Hypergraph matching

Hypergraph matching is the problem of finding a largest collection of pairwise disjoint edges in a hypergraph; it is NP-hard when edges contain 3 or more vertices.

Sep 29, 2026

Hypergraph neural network

A hypergraph neural network (HNN or HGNN) is a graph neural network that operates on hypergraphs, where one hyperedge connects any number of nodes, serving node classification and recommendation.

Hypergraph regularity method

The hypergraph regularity method is an extremal combinatorics technique decomposing any large hypergraph into pseudorandom blocks. It extends Szemerédi's regularity lemma and yields the hypergraph removal lemma.

Hypergraph removal lemma

The hypergraph removal lemma is a theorem of extremal combinatorics stating that a hypergraph with few copies of a fixed hypergraph F can be made F-free by deleting few edges.

Hypergraphia

Hypergraphia: compulsive, extensive writing, classically an interictal feature of temporal lobe epilepsy (Geschwind syndrome, with hyperreligiosity and hyposexuality); also seen in mania and right temporal lobe degeneration.

Sep 19, 2026

Hypergryph

Hypergryph (鹰角网络) is a Chinese video game developer founded in Shanghai in January 2017, best known as the developer and Chinese publisher of the tower defense gacha game Arknights.

Hyperhidrosis

Hyperhidrosis, also known as excessive sweating, is a condition in which a person sweats more than needed for cooling, either all over or in localized areas.

Hyperhomocysteinemia

Hyperhomocysteinemia, elevated blood total homocysteine above 15 µmol/L, affects about 5% of people; caused by folate, B12, or B6 deficiency and MTHFR variants, and B-vitamin lowering does not prevent myocardial infarction or death.

Hypericaceae

Hypericaceae, the St. John's wort family (Hypericaceae Juss., 1789), is a Malpighiales family of herbs and shrubs with gland-dotted leaves; its dominant genus Hypericum holds 521 species, and sister family is Podostemaceae.

Hypericin

Hypericin is a photosensitizing pigment produced by St John's wort (Hypericum perforatum), first isolated in 1939, used as a herbal medicine marker and in photodynamic therapy of cancer.

Hypericum

Hypericum (St. John's worts), genus of Hypericaceae with about 500 yellow-flowered species of herbs and shrubs, cosmopolitan mainly in temperate regions; includes medicinal H. perforatum and invasive weeds.

Hypericum perforatum

Hypericum perforatum (St. John's wort, Klamath weed) is a perennial Hypericaceae herb native from Europe to China and NW Africa, used for mild to moderate depression; extracts show efficacy near standard antidepressants but induce CYP3A4 and P-glycoprotein, causing major drug interactions.