An electroencephalograph is the machine that records the brain’s tiny electric signals. It is the box, the sensors, and the computer — not the wavy picture itself. In real life almost everyone still says EEG for the machine and the test and the printout, so the tidy -graph / -gram split is clearer in dictionaries than in the hospital corridor. You will see the full word in textbooks and equipment lists. It is specialist medical English, not a word friends use. Though actually, older machines drew ink lines on paper; newer ones are mostly a computer screen, but the name did not change.