"Execution is a systematic process of rigorously discussing hows and whats, questioning, tenaciously following through, and ensuring accountability. It includes making assumptions about the business environment, assessing the organization's capabilities, linking strategy to operations and the people who are going to implement the strategy, synchronizing those people and their various disciplines, and linking rewards to outcomes. It also includes mechanisms for changing assumptions as the environment changes and upgrading the company's capabilities to meet the challenges of an ambitious strategy.
"In its most fundamental sense, execution is a systematic way of exposing reality and acting on it."
--from Execution: The Discipline of Getting Things Done (Bossidy, Charan)
I think a good picture of execution is in the Appendices of the movie The Fellowship of the Ring. When you learn how Peter Jackson as the director got everyone and everything working in various departments and then began the process of bringing everything together -- it's truly amazing.
In this way, a business is not much different than making a movie. Your vision/strategy is your main story -- your from point A to point Z -- and your main theme. You still have to make everything come together to make that strategy a reality. Peter Jackson didn't micromanage people. He did, however, concern himself with many details. He trusted key people to do what he knew they were capable of. And he communicated ad naseum.
Execution is knowing what needs to get done and how the whats will get done and then delivering on the promises across multiple departments or personnel. Execution is about getting the right things done in the right ways at the right time in order to achieve success; all the while weaving in and out known and unknown dependencies and environmental factors. Execution is not about doing for the sake of doing. It is about taking action in order to make things happen on the chosen path towards the goal. A thousand mile journey begins with the first step is a true.