Which term describes a one-time multitask job with specific start/end dates and scope?

The term that best describes a one-time multitask job with specific start and end dates and a defined scope is "Project." A project is characterized by its temporary nature, meaning it has a clear beginning and conclusion. It involves a series of tasks aimed at completing a unique objective or delivering a specific result.

In contrast, the other terms provided do not fully encompass the characteristics of a project. A task typically refers to an individual piece of work or action that may not have the same level of complexity or temporal boundaries inherent in a project. An assignment usually implies a directive given to an individual or group but does not necessarily reflect the broader scope and organized structure of multiple tasks that a project involves. A campaign suggests a coordinated series of activities, often in marketing or political contexts, which may not strictly fit the criteria of being a one-time venture with a set scope and timeline. Thus, "Project" captures the essence of a controlled endeavor with particular goals, making it the most appropriate choice.