is when the blood supply to the brain is cut off temporarily, meaning no oxygen
to the brain. Every part of the body needs oxygen to work as it is turned into energy.
When the brain is starved of oxygen, brain cells die, which can damage the parts of the brain that cause our personal bahviour.
For example, one side of the brain controls communication and language. If part of this is damaged, a very talkative person can become quiet and shy, or stop being able to talk altogether.
Other things can be damaged too such as the section that controls the ability to walk.