MILESTONES: The key points in time that sponsors care about, the highest-level accomplishments towards the end goal. Example: Project Requirements Complete and Delivered, Online Reports Tested, Product Deployed and Operational.
OBJECTS: The tangible and concrete deliverables needed to complete the project. They are described using a noun, are clear and understandable by the clients, and are a commonly repeatable item. They are things like a requirements document, one function of a software product, a reusable API, or a single server instance.
TASKS: The action required to produce the deliverable. Tasks are described using a verb and include specific details like who is responsible for the work, how long it will take, and when it will be done. Examples of specific tasks: Modify firewall on vlan 121 to allow ssh traffic, Send scope document draft to project team for review and feedback.
ITS PRO Ontology