Project Action Item is any particular unit of action that is recognized by a project plan. In the most cases it is a terminal element that is displayed on the lowest layer of the WBS – work package that is no longer sub-divided by the project planners, however, individuals who are assigned to do these packages can break them down into smaller steps which make sense in terms of their work (but it is important yet not to exceed limits of the project scope, so minor planning should also be verified by supervisors who are empowered by the project management).
Any actions that are not recognized by the project plan are qualified as “unplanned work” that can cause project scope change, project scope creep or project schedule update. That’s why the project managers should always consider all possible preparatory, secondary, or just “insignificant” actions that are rarely indicated by the project plan, but usually significantly influence the project execution (work speed, emergent costs, staff productivity, etc).
In order to avoid a problematic situation when some tasks are just unregistered in the project plan, (hence have no resources allocated to complete them) the project managers aspire to collect them in a special “pre-planning stage” which prevents qualifying their statuses as unplanned work (please see article what is project pre-planning).