A Coronal Mass Ejection (CME)
A CME is a cloud of hot magnetized  gas, weighing billions of tons, which is launched from the Sun at a speed up to millions of miles per hour. The CME shown in the sequence at the right was launched over an 8-hour period in 1996.
 
CMEs are caused by the breaking apart of magnetic forces. These occur almost every day, but most go off in other directions, not toward Earth.