Shared Meaning
One dictionary every system can read.
Every system names the world for itself. Two of them can hold the same fact and share none of its meaning, which is why joining systems up stays slow, costly, and done by hand, again and again.
The dictionary gives each concept a fixed identity that owes nothing to its name. Translate it, shorten it, rename it, and the identity holds, so everything pointing at it stays correct. Systems built by people who never met land on the same meaning without agreeing on a single word.
From there, meaning accumulates. Each system that joins inherits all that was defined before it, and leaves more behind. It is in production now.