This condition is an abnormal connection between the arteries and veins in the brain. An AVM contains arteries that connect directly to veins without first narrowing down into much smaller blood vessels called capillaries. As a result, blood that is under high pressure is allowed to flow through thin-walled veins. This can interfere with normal blood circulation in the brain and can lead to a hemorrhage.
For more information on AVM please watch this short video below.