A section is a cut through the 3d-model. An elevation is different. It shows the face of something, or perhaps more correct, the projection of an object/s to a plane.
Project Definition: Establishing Scope, Vision and Work Effort. In order to have any realistic shot at a successful project, (delivered on time and on budget) the overall vision and work effort must first be fully defined --- i.e. broken down into small, manageable and actionable parts.
Before you start a project, it is important to know the overall objectives of the project, as well as the scope, deliverables, risks, assumptions, project organization chart, etc. The project definition (or charter) is the document that holds this relevant information.