Ubiquitous Language (DDD)
A Ubiquitous Language is a vocabulary established by (software development) teams that provides semantic contexts of the Domain a software system represents (or parts of represents).
Establishing such a language helps with aligning the development to a model of the Domain with a vocabulary specific to this Domain, in such a way that all participants of the development process (stakeholders, developers, domain experts) have the same understanding of this vocabulary (thus, the Domain). Once established, the Ubiquitous Language is constantly used throughout the project by all participants.
It is used for eliminating communication errors and misunderstandings due to the (often complex) terms of the targeted Domain and ease the transition of such a Domain into a software system.