Project Task Definition
A task can refer to just about any project activity. The length can be short or long, the number of resources can be few or many, and the cost can be quite variable. For the most part, project team members associate the term tasks things they're individually responsible for. Of course, the deliverables from many small tasks ultimately combine to form the deliverable of a larger task.
For example, a project manager has the task of creating the project plan. But this task can require gathering a lot information from a lot of people. Each interaction with these people is a task unto itself. And the information required from these people might require that they each be assigned tasks to pull together the necessary materials.
I've also put together a description of project management fundamentals if you're interested in learning more about this profession.