- For the 2005 hurricane, see Hurricane Epsilon.
Epsilon (upper case Ε, lower case ε) is the fifth letter of the Greek alphabet. In the system of Greek numerals it has a value of 5. "E psilon" ("simple e") was coined to distinguish the letter from αι, which by the medieval period was pronounced the same way.
Letters that arose from Epsilon include the Roman E and Cyrillic Ye.
The lower-case letter ε is used as the symbol for:
- In mathematics, a small positive quantity, usually denoted ε; see limit.
- By analogy with this, the late mathematician Paul Erdős also used the term "epsilons" to refer to children (Hoffman 1998, p. 4).
- In set theory, the limit ordinal of the sequence
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- In computing, the precision of a numeric data type.
- In computer science, the empty string.
- In mathematics, the Levi-Civita symbol.
- In mathematics, set membership (often written ∈ instead of ε), especially in older texts.
- In physics, the permittivity of a medium.
- In automata theory, a transition that involves no shifting of an input symbol.
- In astronomy, the fifth brightest (usually) star in a constellation. See Bayer designation.
- In phonetics, the open or lax mid-front vowel, as in the English word "pet" (/pεt/)
Commerce
Fictional names
- Epsilon Eridani III is the planet that the spacestation Babylon 5 orbited in the eponymous sci-fi television series.