Used primarily regarding health, suggesting no illnesses or medical issues present. After her recovery, she was thrilled to finally get a clean bill of health.
Pro Tip 2/3
Metaphorical Use
Sometimes used metaphorically to talk about non-physical health, like emotional well-being. Mentally, she felt she couldn't claim a clean bill of health.
Pro Tip 3/3
Reassurance
Indicates a relieving confirmation that there are no health concerns to worry about. His parents were relieved to hear that he had a clean bill of health.