Hi Biswaprakash,
Joint MSc PhD means that it gives you a chance to move out from masters degree if you don't want to study. Where is dual degree program is the program where the candidate cannot leave the degree in between and move about. In this is student need to do the MSc and then PhD continuously that is why it is said to be a joint program.
I hope your question has been answered properly.
All the best for your future!
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