In the Soviet Union, work ethic was seen as an ideal to strive for. It basically meant a focus on hard work and diligence (the ability to keep going), for the sake of the work and not because of the rewards of the work.
Today, a lot of people are motivated by a bigger goal, the why of the thing you’re working on. In order to reach your goals, work ethic became the means instead of an end.
There are two possible end goals for a strong work ethic: you either want to get your work done in the least amount of time (so you can spend this time with your family, hobbies or other non-work stuff), or you want to be able to work longer, to get more things done (like you can read in this great piece about President Obama). A strong work ethic is going to support the one you prefer.
If you do some research on work ethic, a number of characteristics pop up: being honest, having a positive attitude, taking initiative, caring about coworkers, doing more than expected, being reliable and responsible, learning new skills and being a team player, to name a few.
The one thing that keeps coming up when reading on work ethic though, is an emphasis on quality. Someone with a great work ethic doesn’t stop with the bare minimum, but goes way beyond what's expected and goes out of his or her way to produce great work. With that, all others follow, because you’re going to need all of the character traits to deliver your absolute best.
Focus on doing great work.