also: せいこ
noun
worldly affairs; the ways of the world
Refers to practical knowledge of society, its customs, and the complexities of human relationships. Often used in contexts discussing experience or sophistication in dealing with people.
彼は世故に長けている。
He is well-versed in the ways of the world.
世故に疎い若者。
A young person who is naive about worldly affairs.
Composed of 世 (world, society) and 故 (reason, circumstances). The exact historical derivation is uncertain, but the combination conveys the idea of the circumstances and affairs of the world.