A Letter of Understanding or LOU is a formal text that sums up the terms and understanding of a contract which mostly has been negotiated up to this point only in spoken form. It reviews the terms of an agreement for a service, a project or a deal and is often written as a step before a more detailed contract is issued.
The LOU may provide for example:
The Letter of Understanding may also introduce key contractual elements, like payment terms.
References
Letter of understanding Wikipedia(Text) CC BY-SA