Cardinality is defined as the number of elements in a set or other grouping. Basically, the more dimensions, or groups, you have in a data set, the ways you can mix and match them grows exponentially. It’s important to remember that when we talk about metric cardinality, we mean the number of unique time series that are produced by a combination of metric names and their associated labels (or, dimensions). The total number of combinations that exist are cardinalities.