Dear student
The ore that are extracted from earth contain earthy impurities like sand stone clay etc. These unwanted impurities in the ore are called gangue.
The mechanical process of removing impurities or we can say gangue from ore is called concentration or dressing of ore. After removal of gangue Concentrated portion of ore minerals are obtained.
dressing and concentration of ore are same thing , there is no difference in that just two names given to same process.
Regards