Metrics can be added to reports, where they determine what data the report computes and displays. But because reports may have any number of filters and attributes that further determine how report data is computed, metrics are contextually impacted by the characteristics of the reports in which they reside.
At times it may be useful to define a metric in a way that determines how the metric will be affected by these contextual report characteristics. This is where MAQL keywords come into play. For example, you could use MAQL to keep a metric from being affected by report filters, or to override report attributes.
MAQL keywords are added to metric syntax in the following order: BY clauses, WHERE clauses, WITHOUT clauses. Note that the order of MAQL keywords is alphabetical.