随机 (suí jī) is an adjective meaning 'random' or 'stochastic', describing events, selections, or processes that occur without a predictable pattern or deliberate choice. The character 随 means 'to follow' or 'according to', suggesting lack of fixed control; 机 originally means 'opportunity' or 'mechanism', but here conveys 'chance' or 'spontaneity'. Together, they express the idea of something unfolding naturally and unpredictably—like drawing names from a hat or generating numbers without bias.

This word is widely used in computing (e.g., 随机数 'random number'), statistics, education (e.g., 随机抽样 'random sampling'), and everyday contexts like games or classroom activities. It carries a neutral, technical tone and is more formal than colloquial alternatives like 碰巧 ('by chance'). While it can modify nouns directly (e.g., 随机事件), it’s rarely used predicatively without additional structure (e.g., not *这件事很随机; instead: 这件事是随机的 or 这件事发生得很随机).