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What is it to be normal?

I've learned in algebra class that

"normal" means a linear operator is commutative with its adjoint;

also we say that $H$ is a normal subgroup of $G$ if $gH=Hg$ for all $g\in G$.

It seems that the word "normal" mostly concerns with the commutative properties, I wonder what other meanings does it have, and why we name it like this~

Any comment will be a help~

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    http://mathoverflow.net/questions/7389/what-are-the-most-overloaded-words-in-mathematics2012-04-27

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