My definition of hard work revolves around complete honesty and a good level of energy being put into some work. It is true that hard work does not always guarantee good results. Hence, I do not associate hard work with good results.
One can really work hard and yet fail to achieve the desired results. Nevertheless, hard work is the key element that needs to be there either way. In my opinion, success is not possible with hard work. So for me, hard work is a combination of practice, dedication, and a good amount of sacrifices both in the form of energy and time.