Here's an informal definition of a task that we use in the Critical Chain world . . .
A task is a chunk of work performed by a resource (or set of resources) that, when complete, yields something (a deliverable, Daniel) that another resource (or set of resources) can use to move the project closer to its objective through his/her/their chunk of work.
Along the line of what Eileen suggests, I liike to advise my clients to use quite verbose task descriptions that explicitly include the tangible delverable (hand-off) of the task so that completion criteria are clear.
Unlike a detailed WBS model, however, we of the Critical Chain Gang like to focus on dependencies (in order to start task B, we must have A, which implies the necessity of a task that delivers A if it doesn't already exist) as a means of defining tasks. A high level WBS to lay out key "milestone deliverables" is sufficient to start to pull a task dependency network together through this method.
I'm curious about examples of non-deliverable-based tasks that you have in mind, Daniel.
