Business Case is one of the primary documents that allow summarizing the need for launching a project and analysing possible alternatives. Throughout the lifecycle of the project this document is used to show the project justification and reasonability. In the Initiation Phase, Business Case is used as a way for making decisions on initiating the project, setting primary goals and defining the cost-benefit ratio.
Project Charter is a primary document that states contains initial requirements for a project to meet the expectations of stakeholders. Formally, Project Charter is an agreement between an organization which is committed to producing a product/service and a customer which requests and receives the product/service. Practically, Project Charter is a planning tool that helps set obligations, rights and privileges for all groups and individual involved within a project.