Wherever possible it should relate to an ‘enforced lack’, arising when a person cannot acquire a good or service because they don’t have the financial or other means to do so.
Lle bynnag y bo modd, dylai ymwneud â ‘diffyg gorfodol’, sy'n codi pan na all person gael nwydd neu wasanaeth am nad oes ganddo'r modd ariannol neu fodd arall i wneud hynny.