It's a circle containing arcane symbols used in ceremonial magic[0,1] also used as a common visual shorthand for magical effects (particularly area of effect spells) in video games and anime[1].

[0]https://en.wikipedia.org/wiki/Magic_circle

[1]https://commons.m.wikimedia.org/wiki/File:Magic_Circle.png

[2]https://tvtropes.org/pmwiki/pmwiki.php/Main/GeometricMagic