What is the difference between a stroke and a seizure?

Much difference. A seizure is a sudden electrical surge in the brain usually related to brain malformation or dysplasia. Seizures can also be related to tumors or metastasis in the brain. Damage to brain by trauma, ischemia, and metabolic disorders can also result in seizure. Stroke is usually from blood vessel clot or narrowing due to atherosclerosis, high blood pressure, and hemorrhage from aneurysm.
See below. A stroke occurs when there is an interruption of blood flow to a part of the brain, either because of a blood clot or because of a ruptured blood vessel. This can lead to permanent damage, as the brain is no longer getting oxygen to that part. A seizure, however, is a greatly increased amount of electrical activity in the brain, and can manifest in a number of ways.