What is this aircraft on the grass in Budapest International Airport?
It has the distinct shape of the 767, and it is indeed a 767 (registration HA-LHB, ex Malev) as can be seen in these photos:


https://www.airliners.net/photo/Malev-Hungarian-Airlines/Boeing-767-27G-ER/4847571
https://www.airliners.net/photo/Untitled-Malev-Hungarian-Airlines/Boeing-767-27G-ER/4850697
https://www.airliners.net/photo/Untitled-Malev-Hungarian-Airlines/Boeing-767-27G-ER/4808155


By the state of the airframe (and the fact that it is illuminated) it is indeed looks like it is being used as a firefighting/rescue training frame.