It can be used as a swear or as a answer to a question when you don't know what to answer but you consider the other person stupid.

It is translated literaly by "your dead mothers people"
Exampels:

Ce morții mă-tii vrei? / What the fuck do you want?

-Cum de a lovit maşina? / How did he hit the car?
-Morții mă-sii?! / I don't know,but he is stupid.
by Guşteru April 18, 2019
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