상식이 · 상식을
common sense; general knowledge
Example
어른에게 인사하는 것은 기본 상식이에요.
Greeting your elders is basic common sense.
Word parts
상 usual+식 recognize
Literally 'ordinary knowledge' — what everyone is expected to know.
Good to know
상식이 없다 means someone lacks common sense — fairly harsh criticism.