What is Data Quality?
Data quality is how well data fits its purpose, usually judged by whether it is accurate, complete, consistent, timely and unique.
Data Quality explained
Accuracy means values are correct; completeness that nothing important is missing; consistency that the same fact is recorded the same way everywhere; timeliness that it is up to date; uniqueness that each real-world thing appears once.
Quality problems cause wrong numbers long before anyone notices: duplicated customers inflate counts, missing dates drop rows from reports, mixed formats break joins.
Example
A customer table with the same person entered three times, one with a blank country, fails the uniqueness and completeness checks.