This is the English-language Wiktionary, where words from all languages are defined in English. June 28 is written as 6/28 in the month/day format, and 6, 2, and 8 are the first three significant digits of τ. Today is Tau Day, which was invented by the American educator and entrepreneur Michael Hartl to promote the use of τ as a mathematical constant in place of 2 π. ( historical ) Short for tau meson, now known as a kaon.Short for tau lepton or tau particle (“an unstable elementary particle which is a type of lepton, having a mass almost twice that of a proton, a negative charge, and a spin of ½ it decays into hadrons (usually pions) or other leptons, and neutrinos a tauon”).

( neurology ) Short for tau protein ( “ a protein abundant especially in the neurons of the human central nervous system that stabilizes microtubules, and when misfolded is associated with forms of dementia such as Alzheimer's and Parkinson's diseases ” ).( mathematics, neologism ) Chiefly written τ: an irrational and transcendental constant representing the ratio of the circumference of a Euclidean circle to its radius, equal to twice the value of pi ( 2 π approximately 6.2831853071).( finance ) A measurement of the sensitivity of the value of an option to changes in the implied volatility of the price of the underlying asset.( astronomy ) Chiefly written τ: used to designate the nineteenth star (usually according to brightness) in a constellation.( Christianity ) A crosier with a Τ-shaped head.A Τ- shaped object or sign a Saint Anthony's cross, sometimes regarded as a sacred symbol.The letter Τ/ τ in the Greek, Hebrew, and ancient Semitic alphabets being the nineteenth letter of the Classical and Modern Greek, and the twenty-first letter of the Old and Ancient Greek alphabets.

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