72,234 articles
Free energy principle
Free energy principle (FEP), Karl Friston's theory of self-organizing biological agents: they minimize variational free energy, a bound on sensory surprise, via perception and active inference; corollary of Bayesian brain ideas, criticized as unfalsifiable.
Free flap surgery
Free flap surgery, or free flap reconstruction, moves a block of tissue such as skin, muscle, or bone to another part of the body, reconnecting its blood supply microsurgically.
Free range
Free range: farming and food-labeling term for livestock with outdoor access, mainly poultry. US voluntary claim requiring daily outdoor access; UK/EU legally defined marketing standards with 12-week (meat) and 16-week (egg) housing derogations removed in 2023-2025.
Free sialic acid storage disease
Free sialic acid storage disease (FSASD), also called Salla disease in its mild form and ISSD in its severe form, is a rare autosomal recessive lysosomal storage disorder caused by SLC17A5 (sialin) defects, causing lysosomal sialic acid accumulation, hypomyelination, ataxia, and elevated urinary free sialic acid.
Free tissue transfer
Free tissue transfer is a reconstructive microsurgical procedure that moves skin, muscle, or bone with its blood supply to a distant site, reconnecting its vessels to recipient vessels.
Free water clearance
Free water clearance is a renal physiology measure of the rate at which the kidneys excrete or retain solute-free water, used to guide hyponatremia treatment.
Free-radical theory of aging
Free-radical theory of aging, also called oxidative stress theory, proposed by Denham Harman in 1954–1956: aging results from cumulative free-radical damage, revised in 1972 to a mitochondrial version, now heavily criticized.
Free-range eggs
Free-range eggs come from uncaged hens with continuous outdoor access during lay, per USDA grademark rules. Distinct from cage-free (no outdoor requirement) and pasture-raised; carries an 18.7% US retail premium and higher hen disease and predation risks.
Free-ranging dog
A free-ranging dog is a domestic dog living around human settlements without effective human restraint, owned or not, and may be the most numerous kind of domestic dog.
Free-Rea study
FREE-REA study, a French prospective multicenter observational trial (NCT02450669) of 1514 extubations in 26 ICUs, 2013-2015; found 10.4% extubation failure, split into airway versus non-airway failure with distinct risk factors.
FREE1
FREE1 (FYVE1, Q9ASS2) is a plant-specific Arabidopsis ESCRT protein, 601 amino acids, that binds PI3P and ubiquitin, joins ESCRT-I via VPS23, and is essential for MVB sorting, autophagy, ABA signaling, and seedling viability.
Freeganism
Freeganism is an anti-consumerist practice of salvaging discarded food, chiefly via dumpster diving, coined by a Food Not Bombs founder in the late 1990s; practitioners also squat, garden guerrilla-style, and avoid paid work.
Freek W.A. Verheugt
Freek W.A. Verheugt is a Dutch cardiologist, emeritus professor of cardiology at Radboud University Medical Centre in Nijmegen, known for the ICTUS trial and anticoagulation research.
Freekeh (فريكة)
Freekeh (فريكة), also farik or frik, is smoky roasted green durum wheat from Levantine and North African cuisine; name from Arabic farak, to rub; protein 11–15%, fiber 12–19%, contains gluten.
Freeman-Sheldon syndrome
Freeman-Sheldon syndrome, also called Freeman-Burian or whistling face syndrome (DA2A), is a rare congenital distal arthrogryposis caused by MYH3 variants, marked by microstomia, pursed lips, H-shaped chin dimple, and hand and foot contractures.
Freesia
Freesia (Freesia Eckl. ex Klatt) is a genus of 16 cormous Iridaceae species native from Kenya to South Africa, named for Friedrich Freese; fragrant cut flowers, over 110 million stems sold yearly in the UK.
Freeze brand
Freeze brand (cryo-branding): livestock identification method developed by R. Keith Farrell at Washington State University in 1966; chilled copper irons destroy melanocytes so white hair regrows, unlike hot-iron brands which scar.
Freeze Etching
Freeze etching (freeze-etching): electron microscopy replica technique; frozen specimens are fractured, surface ice is sublimed under vacuum, and platinum-carbon replicas reveal true cell surfaces and membranes, distinct from cryoprotectant-based freeze-fracturing.
Freeze Fracturing
Freeze fracturing (freeze-fracture EM): a TEM sample-preparation method that fractures a frozen biological specimen under vacuum and makes a platinum-carbon replica; key steps are rapid freezing, fracturing, replication, and cleaning, with optional freeze etching.
Freeze substitution
Freeze substitution dehydrates and chemically fixes a frozen biological specimen at low temperature with a solvent such as acetone, producing a resin-embeddable sample for electron microscopy.
Fregoli delusion
Fregoli delusion, or Fregoli syndrome, is a rare delusional misidentification syndrome in which a familiar person is believed to be disguising themselves as strangers; first described by Courbon and Fail in 1927, named after quick-change actor Leopoldo Fregoli, and linked to right-hemisphere frontal lesions in secondary cases.
Freiberg disease
Freiberg disease (Freiberg infraction, Freiberg-Köhler syndrome) is osteonecrosis of a metatarsal head, usually the second, in adolescent females (5:1 female ratio). Described by Freiberg in 1914; staged by Smillie I–V; treated conservatively first, then with osteotomy or osteochondral grafting.
Fremanezumab
Fremanezumab (Ajovy, Teva) is a humanized anti-CGRP monoclonal antibody for migraine prevention; FDA-approved 2018 for adults, 2025 for children 6–17, dosed 225 mg monthly or 675 mg quarterly.
Fremitus
Fremitus (vocal or tactile fremitus) is a voice-produced vibration palpated on the chest wall; increased over lung consolidation such as pneumonia, decreased over pleural effusion, pneumothorax, or emphysema, with low sensitivity but high specificity.
French Bulldog
French Bulldog (Bouledogue Français): small flat-faced companion breed developed in 1880s Paris from English Toy Bulldogs; bat ears, FCI Group 9; AKC's top US breed since 2022; major health concern is BOAS.
Frenectomy
Frenectomy (frenulectomy): complete surgical removal of an oral frenulum, related to frenotomy and frenuloplasty. Main indications are ankyloglossia with breastfeeding difficulty and aberrant labial frenum causing diastema or gingival recession; evidence for non-breastfeeding indications is weak.
Freneslerbart
Freneslerbart (freneslerbart/mevonlerbart, REGN1908-1909) is Regeneron's 1:1 cocktail of two fully human IgG4 monoclonal antibodies against the cat allergen Fel d 1, studied as single-dose passive immunotherapy for cat-allergic rhinitis and asthma.
Frenotomy
Frenotomy is a minor surgical procedure that divides the lingual frenulum, the tissue anchoring the tongue to the mouth's floor, to treat tongue-tie restricting breastfeeding in infants.
Frenulum
A frenulum (plural frenula, also frenum) is a small fold of tissue anchoring one movable body structure to another, found in the mouth, genitals, digestive tract, and brain.
Frenulum breve
Frenulum breve, or short frenulum, is a congenital or acquired shortening of the penile frenulum causing painful erections, tearing, and sometimes premature ejaculation; treated with stretching, steroid creams, or frenuloplasty.