Cardinality
How many rows on one side of a relationship can match rows on the other side.
Why it matters
Cardinality affects how data is matched, interpreted or acted on in real work. Understanding the term helps you choose the right tool and avoid silent assumptions in reports.
Practical check
When this concept appears in a spreadsheet, query or workflow, ask what one row represents, which values are allowed, and what should happen when data is missing or duplicated.