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I have started seeing the "∈" symbol in math. What exactly does it mean?

I have tried googling it but google takes the symbol out of the search.

Jyrki Lahtonen
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Locke
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    It means "belongs to". For instance $x\in A$ means that the element $x$ belongs to $A$. – Stefan Hansen Jun 25 '14 at 05:27
  • By pure coincidence I was just searching how to input this symbol in mathjax! – Chinny84 Jun 25 '14 at 05:34
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    You could try googling "[mathematical symbols](http://en.wikipedia.org/wiki/List_of_mathematical_symbols)"... –  Jun 25 '14 at 05:46
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    Google doesn't support this at the moment, but Wikipedia does. Enter it in the search or put it in the URL. Take these examples: [∈](http://en.wikipedia.org/wiki/∈), [∪](http://en.wikipedia.org/wiki/∪) and [∩](http://en.wikipedia.org/wiki/∩). – Steve Klösters Jun 25 '14 at 09:47
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    $8$ up votes for this :O –  Jun 25 '14 at 11:41
  • @PraphullaKoushik Haha, now it's 15 –  Jul 22 '15 at 00:36
  • Google will search unicode (maybe it didn't in 2014). https://www.google.com.au/search?q=what+is+%E2%88%88&oq=what+is+%E2%88%88&aqs=chrome..69i57j69i65l3.32479j0j7&sourceid=chrome&ie=UTF-8 – wide_eyed_pupil Aug 06 '17 at 14:46
  • the symbol looks like $e$, as in $e$lement – J. W. Tanner Dec 03 '20 at 02:40

3 Answers3

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$\in$ means '(is) an element of'

For instance, 'Let $a\in A$' means 'Let $a$ be an element of $A$'

http://en.wikipedia.org/wiki/Element_(mathematics) might help you too

Hippalectryon
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  • Being only a freshman going into Honors Algebra Two, I don't understand the concept. But thanks for the answer, even if I don't understand the concept at least I know what it means. – Locke Jun 25 '14 at 05:31
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    @Locke Look at the link I added too – Hippalectryon Jun 25 '14 at 05:32
  • Thanks for the link. The information on that Wiki really cleared it up for me. – Locke Jun 25 '14 at 05:35
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    An added note, since the wiki article does not mention it: one can look at ∈ meaning 'is' through the prism of sets representing the common property held by all its elements. e.g. Even = {0,2,4,..} and 'a ∈ Even' can be read as 'a is Even' – Henry Henrinson Jun 25 '14 at 11:37
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$\in$ means "Element of".

For example, $a \in A$ means Element of: $a$ is in $A$.

A numeric example would be: $\color{red}3 \in \{1, 2, \color{red}3, 4, 5\}$.

M. Winter
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BBot
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∈ (mathematics) means that it is an element in the set of… For eg...x ∈ ℕ denotes that x is within the set of natural numbers.

The relation "is an element of", also called set membership, is denoted by the symbol "∈". Writing {\displaystyle x\in A} x\in A means that "x is an element of A". Equivalent expressions are "x is a member of A", "x belongs to A", "x is in A" and "x lies in A". The expressions "A includes x" and "A contains x" are also used to mean set membership, however some authors use them to mean instead "x is a subset of A".

Another possible notation for the same relation is {\displaystyle A\ni x,} A\ni x, meaning "A contains x", though it is used less often. The negation of set membership is denoted by the symbol "∉". Writing {\displaystyle x\notin A} x\notin A means that "x is not an element of A".

Srishti Chauhan
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  • "contains" and "lies in" are also a very bad words to use here, as it refers to inclusion, not set membership-- two very different ideas. – richard1941 Nov 10 '19 at 03:21