It's referring to the "ubiquitous language" concept popularized by the Domain driven development (DDD) literature. The assumption is that in every business there is an existing language, i.e. a set of terms that refer to the business concepts and are used by all employees when taking about goods, processes and so on.

Developers should take care to elicit this language from their colleagues and use it in their code instead of using whatever terms come to their mind when they need to name things.