Execute is a verb that is made up of only 7 letters. However, they may be the most critical seven letters imaginable when it comes to ultimately determining the success or failure of a given project, or the success or failure of a given phase within said project. The act of executing refers to the act of directing, accomplishing, managing, and completing all phases and aspects of work for a given project. The act of execution begins the moment the project is initiated, and continues throughout the entire process right up until all deliverables for a given project have been completed and ultimately provided to the client whoever that may be. The art of execution in the most time and cost effective manner can not only provide the most likely chance of project success but also can save the client significant amounts of time and possible money in the process of getting there.
This term is defined in the 3rd and the 4th edition of the PMBOK.