I had a dream about my mother. In my dream she was dead and in a coffin,her face was starting decompose. What can this mean?

There are several possiblilites when we dream of the death of a relative.

Firstly it could reflect a significant change or ending to some situation or certain feelings between you.

It could indicate a fear of losing that person. This could be a literal fear of them dying, say if they are ill or elderly, or a fear of losing something emotional from them like their support.

It could also indicate some feelings towards them that have died or we want to get rid of, such as anger.

Your feelings during the dream and the situation between you should help you work out which is more likely. The fact that she was in a coffin and starting to decompose suggests that you feel whatever is behind this you want to be, or fear will be, or has been, rapid and final.