Aneurysms are abnormal bulges or dilations in the wall of a blood vessel, typically occurring in arteries. They can form in various parts of the body, most commonly in the brain (cerebral aneurysms) or the aorta (aortic aneurysms). If an aneurysm ruptures, it can lead to serious complications, including internal bleeding, stroke, or even death. Risk factors include high blood pressure, smoking, and genetic predispositions.