Have to get involved in this discussion, because I can't let these 2 comments pass.
"MD-80 is just the common marketing name"
"Another one. AA has DC-9-82 and DC-9-83s. Call them by the marketing name if you will, they are still DC-9s. "
There is a reason why the DC-9-80/1/2/etc. became MDs. Probably the same reason why the DC-3/4/6/7/8/9s were know as DC and not MD; but a marketing name? C'mon guys..... bit of History 101 won't hurt anyone:
"As 1966 drew to a close, the Douglas Aircraft Company had many orders to fill, and it was the largest aircraft industry employer in California. At the same time, McDonnell was the largest employer in Missouri and was firmly established as an aircraft production giant.
However, startup and production costs for the DC-8 and DC-9 were straining the Douglas Aircraft Company resources. Moreover, for some time McDonnell had wanted to build commercial transports and had talked about merging with Douglas as early as 1963. He was in the best position to submit the winning offer when, in December 1966, the Douglas board of directors sent out bid invitations for possible merger prospects.
The merger of the two companies was official on April 28, 1967. James Smith McDonnell, then 68, was chairman of the board of directors and CEO of the new McDonnell Douglas Corporation. Donald Douglas Sr., 75, was honorary chairman of the merged corporation. Donald Douglas Jr., 46, continued as president of the Douglas component.
On Aug. 29, 1970, the DC-10, the last of the Douglas transports, made its first flight. By then the two powerful airplane concerns had merged, so all subsequent models had the "MD" designation. On Oct. 18, 1979, the DC-9-80 "Super 80" made its first flight. With new wings, new engines and a longer fuselage than the other DC-9s, it was redesignated MD-80 and became the cornerstone for a new series of jetliner models."
Wanna know more: http://www.boeing.com/companyoffices/history/mdc/