Two distinct meanings: (1) 'second / twice' as ordinal/counter, often as 第二次 or 再一次; (2) the math sense - 二次方程 (quadratic equation), 二次函数 (quadratic function). Also forms 二次元 (erciyuan), the slang for anime / 2D culture.
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If you see 二次 in tech or fan circles, it's almost always part of 二次元 (erciyuan, '2D dimension') - the world of anime, manga, and games.
