A business glossary answers "what does this word mean here". Not in general, not in the industry — here, in this company, for reporting purposes. Each entry has a definition, an owner who approved it, the calculation if it is a measure, and ideally the systems and reports where it is implemented. The glossary is where a governance program first becomes visible to people outside it, which makes its quality disproportionately important.
In practice. A glossary earns its existence the first time it settles an argument. Start with the twenty terms that appear in board reporting and are known to be disputed — churn, active customer, revenue, headcount, on-time delivery — and get each one to a single approved definition.
Where it goes wrong. The glossary is built as a completeness exercise, in a tool nobody has in their daily workflow, so definitions are written once and never consulted. A glossary that is not reachable from where people work — the BI tool, the intranet search, the catalog — is a document, not a control.