also: せいじ
noun
worldly affairs; ways of the world
Refers to practical knowledge about society, customs, and how the world works, often used in phrases like 世事に疎い (ignorant of the ways of the world) or 世事に長ける (well-versed in worldly matters).
彼は研究に没頭していて、世事に疎い。
He is so absorbed in his research that he is ignorant of worldly affairs.
祖母は年を取っても世事に明るい。
Even in old age, my grandmother is well-informed about the ways of the world.
Compound of 世 (world, society) and 事 (matters, affairs). The reading せじ is a standard on'yomi combination, while せいじ is an older or alternate reading that is now rare.