They are contributions to the locality that a developer is required to make in order to receive permission to proceed with a project. These contributions may sometimes be only indirectly related to the project itself. Examples are school sites, road improvements and parks. In housing projects, such fees may be charged for the use of schools too. Mitigations are fees charged by the locality supposedly to offset specific public costs resulting from a proposed development.
Examples are traffic mitigations, school mitigations and open space mitigations.
These are sometimes referred to as impact fees. Proffers are required contributions to the community that are only indirectly related to the project for which the developer is requesting permission. Examples are park or school sites, or construction of roadways that serve areas other than the development concerned. Exactions are supposed to be connected to the project for which the developer is seeking permission by some sort of nexus or functional relationship. However, communities often ask for benefits with very weak connections, and developers may be reluctant to fight those requests in court for fear of alienating the local authorities with whom they must work in the future.