MarkLogic Geo Data Services (GDS) is a set of modules that can be added to your MarkLogic application to enable a rich set of geospatial query capabilities against a MarkLogic database. Generally, you will add GDS to your MarkLogic application because you are either using the MarkLogic Koop Provider or the MarkLogic GeoTools Plugin.
Please see the user guide for instructions on installing and using GDS.