There is a very practical and simple definition Good and Bad in Vedic thought. It starts by recognizing that these are relative terms. An electric toaster for example is good for cooking breakfast, but bad as a bath toy. The goodness or badness of anything is relative to what it is used for.
Next, the Vedas clarify what life is used for. Life is used to attain the paramount happiness, they say. So things which help us attain this happiness are “good” and things which block us from attaining the same are “bad.”
The Vedas also give us help setting our aim on what the “paramount happiness” is. It very thoroughly and elaborately goes to great lengths to explain that in the end emotions are what a living being enjoys or suffers. Happiness does not really come from objects, it comes from emotions – which may or may not be connected to objects. Objects are incidental. The emotions are essential.
Now, the question is, which emotions are the happiest and most joyful. The Vedas declare that love is the king of all such emotions. It goes further to explain that love which is perfectly purified of all selfishness is the paramount happiness. The pinnicle of paramount happiness, in the Vedic opinion, is to experience this selfless love in relationship with the divine.
That is what life is meant for. Now we have the relative frame of reference to say what is “good” and what is “bad.” In Vedic thought anything which expresses and encourages selfishness is one or another shade or intensity of “bad.” Conversely, anything which is an expression or cultivation of selflessness is “good.”