what does this symbol mean?

Math and science symbols

The letters and signs used in maths, science and computing, and what each one stands for.

Math and science symbols are the letters and signs used in formulas. The collection holds the Greek letters: a page for each of the 24, from alpha to omega, and two for notation read beside them, nabla (∇) and bra-ket notation.

Greek letters 27 symbols

All 24 letters of the Greek alphabet, their names and sounds, and what each one stands for in maths, science and AI.

What a letter’s page gives

Each page gives the letter’s name and how it is said, its capital and small forms with their Unicode code points, and what it stands for in maths and science. Sections on AI and on quantum physics appear only where the letter has an established use there, such as θ for a model’s parameters in Stanford’s CS229 notes, or ψ for a wave function in OpenStax’s University Physics. Where the names differ, the page says so: the University of Arizona’s guide gives beta’s Modern Greek name as Vita, with a v.

One letter, several uses

σ is a population’s standard deviation in OpenStax’s Introductory Statistics, a surface charge density in NIST’s Guide for the Use of the SI, and the Stefan–Boltzmann constant in NIST’s CODATA values. λ is a wavelength in OpenStax’s Chemistry and the regularization rate in Google’s machine-learning glossary. Each page lists the uses with who writes them.

Letters that are also other characters

Some letters have look-alikes with code points of their own, and Unicode’s charts cross-refer each pair: the micro sign µ and mu, the increment sign ∆ and capital delta, n-ary summation ∑ and capital Σ, n-ary product ∏ and capital pi, and the ohm sign Ω and capital omega. For the ohm, Unicode prefers the capital omega itself. NIST’s guide prints Ω upright when it is the ohm and in italic when it stands for a solid angle. As an SI prefix, μ is micro, a millionth (10⁻⁶).

How the pages are arranged

The Greek letters hub lists the letters in alphabetical order, then the two notation pages. ∇ is an inverted delta, not a letter, and William Robertson Smith suggested its name, nabla, after an Assyrian harp. Bra-ket notation is Paul Dirac’s, from 1939: it writes a quantum state as a ket, |ψ⟩.

Sources

  1. Dirac’s Bra and Ket Notation (8.05 Quantum Physics II lecture notes, B. Zwiebach), MIT OpenCourseWare, Fall 2013, Massachusetts Institute of Technology, Secs. 1, 2, 2.2; Secs. 2, 2.2
  2. CS229 Lecture Notes, Andrew Ng and Tengyu Ma, Stanford University, Part I, chapter 1
  3. University Physics Volume 3, 7.3 The Schrödinger Equation, OpenStax (Rice University), Section 7.3
  4. Modern Greek Alphabet And Phonetics, University of Arizona, Center for Middle Eastern Studies, Letter table
  5. Introductory Statistics 2e, 2.7 Measures of the Spread of the Data, OpenStax (Rice University), Section 2.7
  6. Guide for the Use of the International System of Units (SI), NIST Special Publication 811 (2008), National Institute of Standards and Technology, Sec. 8.6.4 note (c); Sec. 10.2.1 note 1
  7. CODATA Value: Stefan-Boltzmann constant, 2022 CODATA recommended values, National Institute of Standards and Technology, Value
  8. Chemistry 2e, 6.1 Electromagnetic Energy, OpenStax (Rice University), Section 6.1
  9. Machine Learning Glossary, Google for Developers, lambda; regularization rate
  10. C1 Controls and Latin-1 Supplement (code chart, Range 0080–00FF), The Unicode Standard, Version 18.0, Unicode Consortium, C1 Controls and Latin-1 Supplement, 00B5
  11. Greek and Coptic: Range 0370–03FF (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, Greek and Coptic, pp. 39–41; Greek letters; variant letterforms; Greek capital and small letters
  12. Letterlike Symbols: Range 2100–214F (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, Letterlike symbols
  13. Metric (SI) Prefixes, U.S. National Institute of Standards and Technology, SI prefixes table
  14. Earliest Known Uses of Some of the Words of Mathematics (N), Jeff Miller, MacTutor History of Mathematics, University of St Andrews, NABLA
  15. A new notation for quantum mechanics (P. A. M. Dirac), Mathematical Proceedings of the Cambridge Philosophical Society 35(3), 416–418 (1939), Cambridge University Press (Cambridge Core), Abstract; issue details
  16. A new notation for quantum mechanics (P. A. M. Dirac), full text, Mathematical Proceedings of the Cambridge Philosophical Society 35(3), 416–418 (1939), Instituto de Física de São Carlos, Universidade de São Paulo (course copy), p. 418
  17. 8.06 Lecture Notes 3: Entanglement, density matrices and decoherence (A. W. Harrow), MIT 8.06, Spring 2016, Massachusetts Institute of Technology, Secs. 1.2, 2.2.1

Last reviewed September 30, 2026 by Rory Hansen. How we research