Editing Theta (section)

==Mathematics and science==
{{^|This is a disambiguation section, so references are in the linked target articles per [[MOS:DABNOLINK]].  Definitions WITHOUT a link, however, DO require a citation!}}

===Lower case===
The lowercase letter θ is used as a symbol for:
*A [[angle|plane angle]] in geometry<ref>{{Cite web |last=Weisstein |first=Eric W. |title=Angle |url=https://mathworld.wolfram.com/Angle.html |access-date=2025-02-01 |website=mathworld.wolfram.com |language=en}}</ref>
*[[Angle]] (bold) and angular separation in physics<ref>{{Citation |last=Elert |first=Glenn |title=Special Symbols |date=2023 |work=The Physics Hypertextbook|quote='''ϴ''','''φ''',ϴ,φ angle, angular displacement, angular separation, rotation angle |url=https://physics.info/symbols/ |access-date=2025-02-01 |publisher=hypertextbook |language=en}}</ref>
*An unknown angular variable in [[trigonometry]]
*A [[theta function|special function]] {{math|''ϑ''(''z''; ''τ'')}} of several complex variables θ.
*The first [[Chebyshev function]] {{math|''θ''(''x'')}} in prime number theory<ref>{{Cite web |last=Weisstein |first=Eric W. |title=Chebyshev Functions |url=https://mathworld.wolfram.com/ChebyshevFunctions.html |access-date=2025-01-24 |website=mathworld.wolfram.com |language=en}}</ref>
*The [[potential temperature]] in [[meteorology]]<ref>{{Cite book |last1=Holton |first1=James R. |title=An introduction to dynamic meteorology |last2=Hakim |first2=Gregory J. |date=2013 |publisher=Academic Press |isbn=978-0-12-384866-6 |edition=Fifth |location=Amsterdam |pages=87 |quote=Since potential temperature θ is conserved following the motion in adiabatic flow, a parcel of air which movees adiabatically will remain on the same potential temperature surface.}}</ref>
*Dimensionless temperature in heat [[transport phenomena]]<ref>{{Cite book |title=Convection and Conduction Heat Transfer |date=2011 |publisher=IntechOpen |isbn=978-953-307-582-2 |editor-last=Ahsan |editor-first=Amimul |location=Erscheinungsort nicht ermittelbar |pages=57 |quote=θ   dimensionless temperature,...}}</ref>
*The score of a test taker in [[item response theory]]<ref>{{Cite book |last1=van der Linden |first1=Wim J. |title=Handbook of Item Response Theory, Three Volume Set |last2=Hambleton |first2=Ronald K. |date=2018 |publisher=CRC Press |isbn=978-1-4665-1439-3 |edition=1st |series=Chapman & Hall / CRC Statistics in the Social and Behavioral Sciences |location=Boca Raton |pages=section 10.2 |quote=''θ''{{sub|p}} is test taker p's factor score or latent trait parameter.}}</ref>
*Theta Type Replication: a type of bacterial [[DNA replication]] specific to circular [[chromosomes]]
*Threshold value of an [[artificial neuron]]
*A [[Bayer designation]] letter applied to a star in a constellation; usually the eighth star so labelled but not necessarily the eighth-brightest as viewed from Earth<ref>{{Cite book |last=Bakich |first=Michael E. |title=The Cambridge guide to the constellations |date=1995 |publisher=Cambridge University Press |isbn=978-0-521-46520-5 |location=Cambridge |pages=109 |quote=To designate the 24 brightest stars in the constellation, Johannes Bayer used the lowercase letters of the Greek alphabet:}}</ref>
*The [[statistical parameter]] frequently used in writing the [[likelihood function]]<ref>{{Cite book |last1=Casella |first1=George |title=Statistical inference |last2=Berger |first2=Roger W. |date=2024 |publisher=CRC Press |isbn=978-1-032-59303-6 |edition=Second |series=CRC texts in statistical science series |location=Boca Raton |pages=8 |quote=Likelihood is the most directly accessible inferential element for estimation statements about θ conditional on f...}}</ref>
*The [[Watterson estimator]] {{mvar|θ&#770;<sub>w</sub>}} for the [[population mutation rate]] in [[population genetics]]<ref>{{Cite book |last=Hösel |first=Volker |title=Mathematical population genetics and evolution of bacterial cooperation |date=2020 |publisher=World Scientific |isbn=978-981-12-0549-1 |location=New Jersey |pages=75}}</ref>
*Indicates a minimum optimum integration level determined by the intersection of GG and LL schedules (The GG-LL schedules are tools used in analyzing the potential benefits of a country pegging their domestic currency to a foreign currency.)<ref>{{Cite book |last=Reszat |first=Beate |title=European financial systems in the global economy |date=2005 |publisher=Wiley |isbn=978-0-470-87056-3 |location=Chichester, West Sussex, England ; Hoboken, NJ |pages=223–224 |quote=As a consequence, the critical level for joining shifts from θ to θ' -...}}</ref>
*The reserve ratio of banks in economic models<ref>{{Cite book |title=Macroeconomics and development: Roberto Frenkel and the economics of Latin America |date=2016 |publisher=Columbia University Press |isbn=978-0-231-17508-1 |editor-last=Damill |editor-first=Mario |series=Initiative for policy dialogue |location=New York |quote=...θ and θ{{sup|*}} are reserve ratios in DC and FC... |editor-last2=Rapetti |editor-first2=Martín |editor-last3=Rozenwurcel |editor-first3=Guillermo}}</ref>
*The [[ordinal collapsing function]] developed by [[Solomon Feferman]]<ref>{{Cite journal |last=Feferman |first=Solomon |author-link=Solomon Feferman |date=2010 |editor-last=Schindler |editor-first=Ralf |title=The proof theory of classical and constructive inductive definitions. A 40 year saga, 1968–2008. |url=https://math.stanford.edu/~feferman/papers/id-saga.pdf |journal=Ways of Proof Theory |pages=7–30|doi=10.1515/9783110324907.7 }}</ref>
*The [[Heaviside step function]]<ref>{{Cite web |last=Weisstein |first=Eric W. |title=Heaviside Step Function |url=https://mathworld.wolfram.com/HeavisideStepFunction.html |access-date=2025-01-24 |website=mathworld.wolfram.com |language=en}}</ref>
*In [[pharmacology]], the fraction of ligand bound to a macromolecule based on the [[Hill equation (biochemistry)|Hill Equation]]<ref>{{Cite book |title=Applications of Calorimetry in a Wide Context: Differential Scanning Calorimetry, Isothermal Titration Calorimetry and Microcalorimetry |date=2013 |publisher=IntechOpen |isbn=978-953-51-0947-1 |editor-last=Ali Elkordy |editor-first=Amal |location=Erscheinungsort nicht ermittelbar |pages=75 |quote='''Saturation fraction, θ.''' The fraction of the total number of sites of the macromolecule occupied by ligand molecules.}}</ref>
*The angle of the incident beam during [[X-ray diffraction]]<ref>{{Cite book |title=Biochar: a guide to analytical methods |date=2017 |publisher=CSIRO Publishing |isbn=978-1-4987-6553-4 |editor-last=Singh |editor-first=Balwant |location=Clayton South |pages=246 |quote=θ is the angle between the incident x-ray beam and the diffracting plane |editor-last2=Arbestain |editor-first2=Marta Camps |editor-last3=Lehmann |editor-first3=Johannes}}</ref>

===Upper case===
The uppercase letter Θ is used as a symbol for:
*[[Theta function|Theta functions]]<ref>{{Cite web |title=DLMF: Chapter 20 Theta Functions |url=https://dlmf.nist.gov/20 |access-date=2025-01-31 |website=dlmf.nist.gov}}</ref>
*[[Dimensional analysis|Dimension]] of [[temperature]], by [[SI unit|SI standard]] (in italics)<ref>{{Cite book |last=Lemons |first=Don S. |title=A student's guide to dimensional analysis |date=2017 |publisher=Cambridge University Press |isbn=978-1-107-16115-3 |location=New York |pages=50 |quote=The physics of heat transfer requires two dimensions, temperature Θ and heat H, beyond those that characterize non-equilibrium dynamics.}}</ref>
*An asymptotically tight bound in the [[analysis of algorithms]] ([[big O notation]])
*A certain [[ordinal number]] in [[Θ (set theory)|set theory]]
*[[Pentaquark]]s, exotic [[baryon]]s in [[particle physics]]
*A [[Electroencephalography|brain signal frequency]] (beta, alpha, theta, delta) ranging from 4–8&nbsp;Hz
*One of the variables known as [[Greeks (finance)|"Greeks" in finance]], representing time decay of options or the change in the intrinsic value of an option divided by the number of days until the option expires<ref>{{Cite book |last=Ursone |first=Pierino |title=How to Calculate Options Prices and Their Greeks: Exploring the Black Scholes Model from Delta to Vega |date=2015 |publisher=John Wiley & Sons, Incorporated |isbn=978-1-119-01162-0 |edition=1st |series=The Wiley Finance Series |location=Newark |pages=2 |quote=Θ (time decay): the price change of an option in relation to time;}}</ref>