Clean

Any residue remaining is within an acceptable level

Clean is defined in PDA TR29, Points to Consider for Cleaning Validation, as "Having product residues, process residues, and environmental contaminants removed to an acceptable level". Typically, health-based limits are set for equipment which determines how much of a specific residue is allowed to remain on the equipment and it must be demonstrated that any residue remaining is below said limit. Usually, visual inspection, swab sampling, and rinse sampling are used alongside a validated analytical method to determine if the surface is clean.