I can't search it on google, because it doesn't support symbols like these.
It might have to do with binary operations, I think.
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5Without some context, it could mean almost anything. Often $f\circ g$ means the function or operation that results from performing the operation $g$ followed by the operation $f$. – MJD Jul 02 '13 at 17:10
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2Please tell us where you are encountering this symbol. – Thomas Andrews Jul 02 '13 at 17:17
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As an expoent it means "degree": $45{{}^\circ}=\pi /4$. – Américo Tavares Jul 02 '13 at 17:43
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It also means "connected component containing the identity". – M Turgeon Jul 02 '13 at 18:43
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Since you mention "binary operation", I'll point out some of the more common meanings of $\circ$ when speaking of functions and/or binary operations.
The symbol "$\circ$" denotes the composition of functions, composition of relations, or the composition of permutations, and more generally, denotes a binary operation, sometimes described as a law of composition, where $f\circ g$ is the function or operation resulting from performing the function/operation $g$, followed by the function/operation of $f$.
When denoting function composition, for example, if we are given that $f(x)$ and $g(x)$ are functions of $x \in \mathbb R$ such that: $f: \mathbb R \to \mathbb R,\; g:\mathbb R \to \mathbb R$, then $\;f\circ g: \mathbb R \to \mathbb R$ can be expressed as $$(f\circ g)(x) = f(g(x))$$
amWhy
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Mohamed: does this help? You can accept an answer, even to a question that's on hold. You can also comment, or ask for clarification: I'm here if you need me. – amWhy Jul 05 '13 at 01:01
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Usually composition of functions as stated in the other answer, but also can mean Hadamard/Schur/entrywise matrix product.
Ross B.
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