결함이 · 결함을
defect, flaw, fault
Example
그 회사는 자동차 결함 때문에 리콜을 했습니다.
The company issued a recall because of car defects.
Word parts
결 lacking+함 pitfall
Literally 'something missing, a pitfall.'
Good to know
결함 is for flaws in products or systems; for personal shortcomings, 단점 is more common.