Poppy seed is the seed from the poppy plant (Papaver somniferum). It's used in cooking. The seed pod contains opium, a source of opiates such as morphine.
Poppy seeds don't contain opiates naturally, but the seeds can become coated with opiates during harvesting or by insects. Because of this, the amount of opiates on poppy seeds varies widely. Ready-to-eat poppy seeds have been processed to remove opiates.
People use poppy seed to diagnose an abnormal connection between the bowel and the bladder (vesicoenteric fistula). It's also used for cough, insomnia, and many other conditions,