Learn in the textbookData Operations and Levels of Measurement
DefinitionData aggregation (データの集計) is the operation of combining individual records to suit a purpose and working out values such as the total, the count and the average.
ExplanationRecord-by-record data makes the overall trend hard to see, so aggregation condenses it into a handful of numbers. You can also split the data into groups by an item such as region or month and work out a subtotal for each group. In spreadsheet software, the functions that add up values or count entries carry out this operation.
AnalogyIt is like adding up a month of household spending by category and listing how much went on food and how much on transport.
Memory hookThe Japanese word 集計 joins 集 (gather) and 計 (measure), naming the two steps of the job: collect the records, then compute the figures.