1 [map projections] One of the variables that define a specific instance of a map projection or a coordinate system. Parameters differ for each projection and can include central meridian, standard parallel, scale factor, or latitude of origin.
2 [mathematics] A variable that determines the outcome of a function or operation.
3 [ESRI software] In geoprocessing in ArcGIS, a characteristic of a tool. Values set for parameters define a tool’s behavior during run time.