The surface of this hexagon consists of four congruent equilateral triangles.  The hexagon has a circumscribed circle, the center of which is also the center of a rotation with angle 120 degrees, in one sense or the other, that transforms this hexagon into itself.  This center is called the center of the hexagon.
<a href="//commons.wikimedia.org/wiki/User:Baelde" title="User:Baelde">Baelde</a>
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<span class="int-own-work" lang="en">Own work</span>