Stroke occurs when blood flow to the brain is interrupted, depriving brain cells of oxygen and nutrients. There are two main types of stroke - ischemic, caused by blockage of a blood vessel, and hemorrhagic, caused by bleeding. Risk factors include hypertension, diabetes, smoking, heart disease, and age. Diagnosis involves medical history, physical exam, and imaging tests like CT scan or MRI. Treatment depends on the type and severity of stroke, with the goal of restoring blood flow and preventing further brain damage.