What is the difference between product breakdown structure (PBS) and a work breakdown structure (WBS)?

Definition

Short answer: The output of scope management is a specification that may be presented as a product breakdown structure (PBS) showing the deliverables and a work breakdown structure (WBS) showing the work required to produce them. 

Definition from APM Body of Knowledge 7^th edition

Long answer: The output of scope management is a specification that may be presented as a product breakdown structure (PBS) showing the deliverables and a work breakdown structure (WBS) showing the work required to produce them. The planning process will add management activities to the WBS to show the work involved in managing aspects such as risk and communications.  Once a solution has been identified which meets the stakeholder requirements, the scope of the work can be illustrated using a product breakdown structure (PBS) and a work breakdown structure (WBS).

• The PBS is a hierarchical structure* where the main output of the project is placed at the top level. The next level down shows the components that make up the higher level. This process continues to the level of individual products. Each product will have defined acceptance criteria and quality control methods.
• A WBS takes a similar approach but shows the work required to create the products. The lowest level of a WBS shows the activities that would be used to create a network diagram for time scheduling.

*A hierarchical structure by which project elements are broken down, or decomposed. Examples include: cost breakdown structure (CBS), organisational breakdown structure (OBS), product breakdown structure (PBS), and work breakdown structure (WBS).

Introduction to Project Planning

When you are about to start a project, organise an event or launch a new product, good planning is vital. This concise guide describes how project planning integrates with the many disciplines and how it crucial to successful project management.

APM Body of Knowledge 7^th edition

The APM Body of Knowledge 7^th edition is a foundational resource providing the concepts, functions and activities that make up professional project management. It reflects the developing profession, recognising project-based working at all levels, and across all sectors for influencers, decision makers, project professionals and their teams.