There are multiple definitions:

1. hereditary recurrent fever [syndrome](English)

   • rare disease caused by molecular defects in genes involved in the regulation of innate immunity
   • AIDAI, CAPS, FMF, MKD, TRAPS
   • Genetics, Immunology
   • https://doi.org…8/ejhg.2008.253

2. histamine releasing factor(English)

   • constitutively secreted as a monomer, a disulfide-linked dimer, and higher molecular weight oligomers
   • eQTL, GST, HRF, IgE, mRNA, SNP, TCTP, TNF
   • Allergy
   • https://doi.org…90/cells8121515

3. hemodynamic response function(English)

   • CBT, fMRI, OCD
   • Brain (dys)function, Medical imaging, Behavior(al science), Hemodynamics
   • https://doi.org…682-020-00358-8

4. Human Research Facility(English)

   • ISS, OPE
   • Aviation medicine
   • https://doi.org…162456.37962.01

5. hyperreflective focus(English)

   • a term coined to depict hyperreflective dots or roundish lesions within retinal layers visualized through optical coherence tomography
   • AMD, DME, INL, OCT, OCTA, ONL, OPL, SSPiM
   • Biomarker, Ophthalmology
   • https://doi.org…55/2021/6096017

6. hypoxic respiratory failure(English)

   • can be caused by meconium aspiration, pneumonia, sepsis, respiratory distress syndrome, hernia in the diaphragm, persistent pulmonary hypertension
   • FiO2, OSI, PPHN
   • Oxygen, Respiratory system, Pathology, Neonatology
   • https://www.nic…4/11/hrf-en.pdf
   • https://doi.org….1159/000369774

7. harmonic richness factor(English)

   • DRF, EGG, F0, GNE, HNR, H1-H2
   • Signal analysis
   • https://doi.org…OC.2021.3126493