You have created one or more quantity conversion types.
More information: Creating Quantity Conversions Types.
If you want to convert the units of measure of the key figures in the query, you can determine the conversion type for the individual key figures or structure elements in query definition. You can specify how the individual elements (key figures of type Amount) of the query are to be translated. You can specify one quantity conversion type for each element.
Depending on how the target quantity determination is defined in the quantity conversion type, you can either specify a fixed target quantity or a variable that the system uses to determine the target quantity.
See Unit Conversion in Properties of the Selection/Formula.
If a variable is used, the system requests the variable when you execute the query. For information on the procedure, see Setting Variable Target Units of Measure in the Query Designer.