Editing Pi (letter) (section)

== Lowercase Pi ==
The lowercase letter {{pi}} is used as a symbol for:
* The mathematical real [[Transcendental number|transcendental]] (and thus [[Irrational number|irrational]]) [[Pi|constant π]]&nbsp;≈&nbsp;3.14159..., the ratio of a circle's [[circumference]] to its [[diameter]] in [[Euclidean geometry]],<ref>{{Cite web |last=Weisstein |first=Eric W. |title=Pi |url=https://mathworld.wolfram.com/Pi.html |access-date=2025-01-18 |website=mathworld.wolfram.com |language=en |quote=The constant pi, denoted {{pi}}, is a real number defined as the ratio of a circle's circumference C to its diameter}}</ref> exactly half of the circle constant. The letter "{{pi}}" is the first letter of the Greek words {{wikt-lang|grc|περιφέρεια}} 'periphery' and {{wikt-lang|grc|περίμετρος}} 'perimeter', i.e. the circumference.
* The [[prime-counting function]] in mathematics.<ref>{{Cite web |last=Weisstein |first=Eric W. |title=Prime Counting Function |url=https://mathworld.wolfram.com/PrimeCountingFunction.html |access-date=2025-01-18 |website=mathworld.wolfram.com |language=en |quote=The prime counting function is the function {{pi}}(x) giving the number of primes less than or equal to...}}</ref><ref>{{Cite web |title=DLMF: §27.12 Asymptotic Formulas: Primes ‣ Multiplicative Number Theory ‣ Chapter 27 Functions of Number Theory |url=https://dlmf.nist.gov/27.12 |access-date=2025-01-31 |website=dlmf.nist.gov}}</ref>
* [[Homotopy group]]s  in algebraic topology.
* Dimensionless parameters constructed using the [[Buckingham π theorem]] of [[dimensional analysis]].
* The [[hadron]] called the [[pion]] (pi meson).<ref>{{Cite web |title=Pi meson {{!}} subatomic particle {{!}} Britannica |url=https://www.britannica.com/science/pi-meson |access-date=2025-01-18 |website=www.britannica.com |language=en |quote=Also known as: pion}}</ref>
* Often [[inflation]] rate in macroeconomics.<ref>{{Cite web |title=Fisher Equation |url=https://corporatefinanceinstitute.com/resources/economics/fisher-equation/ |access-date=2025-01-18 |website=Corporate Finance Institute |language=en-US |quote=π – the inflation rate}}</ref>
* Sometimes [[Profit (economics)|profit]] in microeconomics.
* A type of [[chemical bond]] in which the p orbitals overlap, called a [[pi bond]].<ref>{{Cite web |title=Pi bond {{!}} Double Bond, Electron Sharing & Hybridization {{!}} Britannica |url=https://www.britannica.com/science/pi-bond |access-date=2025-01-18 |website=www.britannica.com |language=en}}</ref>
* The natural projection on the [[tangent bundle]] on a [[manifold (mathematics)|manifold]].
* The unary operation of [[Projection (relational algebra)|projection]] in [[relational algebra]].<ref>{{Cite web |date=2024-03-25 |title=What are the Unary Operations in Relational Algebra? |url=https://www.geeksforgeeks.org/what-are-the-unary-operations-in-relational-algebra/ |access-date=2025-01-18 |website=GeeksforGeeks |language=en-US |quote=The projection operation is a unary operation that is performed on a relation. A projection operation is used to retrieve all the values of one or more attributes. It is denoted by π.}}</ref>
* Policy in [[reinforcement learning]].
[[File:Polyamory Pride Flag.svg|thumb|right|The earliest [[polyamory]] [[pride flag]] design, created by Jim Evans in 1995, in which the lowercase letter π stands for the first letter of polyamory.]]
* [[Polyamory]] (in the earliest polyamory [[pride flag]] design, created by Jim Evans in 1995, pi stands for the first letter of polyamory).<ref>{{Cite web|url=https://www.thespinoff.co.nz/society/22-04-2019/pretty-poly-why-non-monogamous-relationships-are-all-the-rage/|title=Pretty poly: Why non-monogamous relationships are all the rage|first=Melody|last=Thomas|date=April 22, 2019|access-date=March 24, 2021|archive-date=February 26, 2021|archive-url=https://web.archive.org/web/20210226022106/https://thespinoff.co.nz/society/22-04-2019/pretty-poly-why-non-monogamous-relationships-are-all-the-rage/|url-status=live}}</ref><ref>{{Cite web|url=https://www.goodhousekeeping.com/life/g39944774/lgbtq-flags/|title=21 LGBTQ Flags and What They Symbolize|first=Lizz|last=Schumer|date=May 16, 2022|website=Good Housekeeping}}</ref><ref>{{Cite web|url=https://www.lgbtqnation.com/2022/06/polyamorous-flag-look-like/|title=What does the polyamorous flag look like?|first=Matthias|last=Walsh|website=LGBTQ Nation|date=17 June 2022 }}</ref><ref>{{cite web|title=Jim Evans' Polyamory Pride Flag|url=http://homepage.isomedia.com/~jene/flag.html|archive-url=https://web.archive.org/web/20141110021410/http://homepage.isomedia.com/~jene/flag.html|archive-date=November 10, 2014}}</ref>