careless mistake; honest mistake; slip-up
A mistake made through inattention or absent-mindedness, not through malice or incompetence. Often used when someone forgets something, overlooks a detail, or makes a simple error.
I accidentally sent the wrong document due to a careless mistake.
うっかりミスを防ぐために、チェックリストを作った。
I made a checklist to prevent careless mistakes.