A "briefing" is a term from advertising & PR agencies. It is a document in which the customer explains what their business context, goals and "value demand" is, at what budget etc etc.

Thanks for the link, I will look into it. I worked with use cases and user stories, but user stories will frequently have some gaps in them - and it's in those gaps that misunderstandings occur. I was hoping that there's a universal language to create bullet proof models.