Ubiquitous language is a common language used by both the Domain experts/Business analysts and the Developers to easily communicate across the whole team while avoiding any miscommunication. Ubiquitous language is the heart of Domain Driven Design (DDD). It is a simple domain specific language and highly readable, used in all forms of communications including the code, diagrams, design documents, etc. Ubiquitous language should be able to explain all concepts of that domain, and can explain new terms using already understood terms.

More info: Subtleties of Ubiquitous Language