The most common use of the groupby method is to perform an aggregation. What actually is an aggregation? In our data analysis world, an aggregation takes place when a sequence of many inputs get summarized or combined into a single value output. For example, summing up all the values of a column or finding its maximum are common aggregations applied on a single sequence of data. An aggregation simply takes many values and converts them down to a single value.

In addition to the grouping columns defined during the introduction, most aggregations have two other components, the aggregating columns and aggregating functions. The aggregating columns are those whose values will be aggregated. The aggregating functions define how the aggregation takes place. Major aggregation functions include sum, min, max, mean, count, variance, std, and so on.