This is the administration of barium sulphate (a soft white metal) for radiographic examination of the upper gastrointestinal tract.
Barium sulphate is a barium salt, insoluble in water, and it is opaque to x-rays. Because x-rays can not go through it, an outline of the stomach, bowel or other areas can be easily seen to check for cancers or other suspected disorders.
It is given as a white liquid drink, hence the name, Barium Meal.
A ‘barium enema’ may also be administered to examine the colon.