visibly clean

This term is defined in ECSS-E-ST-35-06C Rev.1 as
absence of surface contamination when examined with a specific light source, angle of incidence, and viewing distance using normal or magnified vision up to ×20

This term is defined in ECSS-Q-ST-70-01C as
absence of surface contamination when examined with a specific light source, angle of incidence and viewing distance using normal or magnified vision