A metric is a computational expression of numerical data (facts or other metrics). For example, you can have metrics representing the average invoice sum or the number of sold items per country.
You can also create metrics from attributes to count the number of individual values of the attribute. For example, if you have an attribute describing the location of a sales department, you may want to know how many different locations you have in total.
Metrics are built using Multi-Dimension Analytical Query Language (MAQL) through either the API or the Metric Editor. In GoodData, you work with the metrics in Analytical Designer when creating visualizations.