Quality has dimensions:
Completeness: Are all expected records present? Missing data breaks downstream aggregations.
Accuracy: Does data match reality? A user's age of is inaccurate.
Timeliness: Is data fresh enough? Yesterday's stock prices are useless for trading.
Consistency: Does data agree across systems? User count shouldn't differ between tables.
Validity: Does data conform to rules? Email fields should contain valid emails.
Uniqueness: No unwanted duplicates? Primary keys must be unique.