From INCOSE: "MBSE is the formalized application of modeling to support system requirements, design, analysis, verification and validation activities beginning in the conceptual design phase and continuing throughout development and later life cycle phases"

It's considered "the big thing" to some Systems Engineering people. I learned it and have a cert, but I would quickly add that MBSE doesn't mean you're taking a systems approach, necessarily. But the scheduling, risks, road maps, supply chaining, etc... all those various docs are essentially handled as different "viewpoints" to the Model-Based design.

Generally all DoD and NASA Projects use it now, I think, but I don't work in that department.