it's mk for Mark , because the MK5 are the 5th generation of golf or jettas
before you get flamed too bad i will just answer your question.
MK - mark aka generation
MK 2, 3, 5, etc - is the actual generation number spanning in number of years.
-your car is a MK4 meaning the fourth generation of production of jetta's spanning in years from 99-05
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