The method used to summarize data.
In general data science terms, an aggregation is "a function or field where the values of multiple rows are grouped together as input on certain criteria to form a single value of more significant meaning or measurement." (Source: Wikipedia)
In Looker Studio, fields can have the following aggregation methods:
Auto is applied by Looker Studio and can't be changed.
None is applied to dimensions and unaggregated metrics. You can change this for metrics in the data source and report. If left as None in the data source, the default aggregation in reports is