Original: Aneurysms most commonly occur in arteries at the base of the brain (the circle of Willis) and in the aorta (the main artery coming out of the heart, a so-called aortic aneurysm).
Simplified: Aneurysms usually happen in arteries at the base of the brain and in the aorta (the main artery coming out of the heart) - this is an aortic aneurysm.