All weapons and items are split up into different qualities that determine it's rarity. It usually cannot be changed. There is 'Normal' and 'Unique', '. All the other qualities,'Vintage', 'Genuine, 'Strange', 'Unusual', 'Collector's', 'Decorated', 'Haunted', 'Community', 'Self Made', and 'Valve', are all gotten on special circumstances and/or have special traits.