Stewardship is the mechanism that turns authority into effect. A council can decide that "revenue" has one definition; stewardship is what finds the four systems where it is calculated differently, gets three of them changed, and documents the fourth as a known exception. As a discipline it is mostly unglamorous: maintaining a glossary, chasing an issue across two teams, explaining the same definition to a new analyst for the fifth time.
In practice. A stewardship model names, per domain, who the owner is, who the stewards are, how a definition change is proposed and approved, and where issues are logged. Written down, that is two pages, and those two pages are the operating model most programs are missing.
Where it goes wrong. Stewardship gets treated as documentation work and measured by glossary term count. Term count is a vanity metric — a glossary of 900 terms nobody looks at is worth less than 40 terms that the reporting team actually uses. Measure use and resolution, not volume.