Difficult, irksome, tedious, boring and unglamorous work or effort needed to achieve success in a business venture, sport or study.
Used in speech as "doing the hard yards" or "putting in the hard yards".
Originated in Australia - New Zealand either in farming or rugby. To create a profitable farm it is necessary to "put in the hard yards" by clearing the land etc. In rugby, to score a try it is necessary for other team members "do the hard yards" by bringing the ball up the field against the opposition's best and brutal efforts so as to create a scoring opportunity
If you want to get fit, lose weight and have a chance to be picked for the team, you need to put in the hard yards down at the gym and at training.