[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.
[mathematics]
A variable that determines the outcome of a function or operation.
[ESRI software]
In geoprocessing in ArcGIS, a characteristic of a tool. Values set for parameters define a tool's behavior during run time.