This is an abnormality of the pattern of breathing.
It consists of cycles of gradual increase in tidal volume, followed by a gradual decrease in tidal volume and a period of apnea (apnoea). In plain English, that means the patient has deepening breaths, followed by shallower and shallower breaths and stops breathing for a short period of time.
This abnormal pattern of breathing can be seen in patients with strokes, head injuries or brain tumours, in patients with congestive heart failure and in otherwise normal people during sleep at high altitudes.
In the very sick patient, it is often a sign of impending death.