Spiffy means smart-looking in a pleasing, put-together way — neat, clean, stylish. It is used for clothes and appearance above all ('a spiffy new suit', 'You look spiffy'), and also for objects that look sharp and new: a spiffy car, a spiffy website, a spiffy little kitchen. The feeling of the word matters as much as the meaning. It is warm, light and a bit old-fashioned, the sort of thing an uncle says. Because of that, younger speakers often use it half-jokingly — saying 'spiffy' about your friend's new haircut is a small joke about sounding like your grandfather, while still being a real compliment. It is much more common in American English than British. Software people have kept it alive in a slightly different way: a 'spiffy' feature means a neat, clever one. There is a related verb phrase, 'spiff up' or 'spiff yourself up', meaning to make something or yourself look better: 'Let me spiff up the slides before the meeting.' That phrase is more used today than the plain adjective.