Combining multiple individual values into summary totals, averages, or counts.
Aggregation reduces a large number of detailed records into a smaller set of summary statistics. Common aggregation functions include sum, average (mean), count, minimum, maximum, and median. Aggregated data is easier to interpret and visualize than raw records.
Example: A dataset of individual property tax payments is aggregated by neighbourhood to produce the total tax revenue per neighbourhood per year. The aggregated result has one row per neighbourhood instead of thousands of individual payment records.
Aggregation is also used to protect privacy: publishing average income by postal code reveals trends without exposing individual salaries.