It is the ability to subordinate one's actions to the realization of a long-term plan. Disciplined people always have a goal in mind. They are also aware of how much they can achieve with their work and persistence if they really want something.
It is a value characteristic of people who are determined and goal-oriented. They are able to give up temporary pleasures in favor of a postponed reward.
Be careful that you don't start demanding too much of yourself. It is possible that at some point we set ourselves too high expectations.