Dew point is the temperature to which air must cool, where the water vapour in the air will condense into water. Thsi will be at a constant barometric pressure.
I did not understand your question.You want to know the definition of DP or ur machines are producing wet product? i.e if air compressors are producing wet air then you have to cool to condense and drain the water.The DP dew point is the temperature at which water vapors convert to drops.If there are more water vapors in process these will condense easily i.e +10C.If less water is there in process then dewpoint will be relatively negative i.e -10.Normally more dry process is required means less water in process.