What does life support mean?

Life support is when the person body is in a really bad shape (like after a really bad car crash or overdose). They put a life support on the person life is supported by the machine- that why it is called a life support; supports life. Sometimes the person ends up relying completely on the machine and will never wake up. The doctor switch off the life support because the person life is dependant on it and they can never come off it- they will never wake up.