Another name for tuberculosis. This is what they meant in the 2001 movie, Moulin Rouge, when they said that Satine had a fatal disease - tuberculosis is usually fatal unless treated with antibiotics ... which would not be available in the era in which the movie was set.
The thing about Moulin Rouge, of course, was how these people so calmly said that Satine had consumption yet stood nearby while she coughed up blood. Equally so for the doctor who so gallantly pronounced that she had consumption right in front of her. Didn't these people know anything about infection control?
Having recently (July 2001) seen a young person with consumption, I can appreciate why they used to call it such. It's like having your organs consumed from within. This 23 year old man was literally coughing his lungs out. Haemoptysis (coughing up blood) by the cupful. Poor guy. Luckily for him, modern anti-tuberculous treatment is pretty good - after less than one week, he had recovered sufficiently such that he was well enough to walk again. Before modern antibiotics, a man in that condition would almost certainly have died.