The initials mean:
JTD -- uniJet Turbo Diesel ('unitjet' was the predecessor to Fiat's later 'multijet' series of diesel engines, which, so far as I know has never been fitted to the current Panda range)
MJT is Multi Jet Turbo, and so is the same as 'Multijet' as all the Mutijet diesels have a turbo.
The Panda diesels are all 1.3 Multijet engines, with a turbo. (really, its only a 1.2 since its 1248cc!)