嘢 (je5) is Cantonese for 'thing / stuff'. 好嘢 pulls double duty: as an interjection it's 'yay! / nice!', and as a noun phrase it literally means 'a good thing'. Classic crowd cheer at HK sports events.
culture
Often stretched as 好嘢！好嘢！in Cantonese opera and TVB drama moments of triumph. Mainland Mandarin equivalent: 好耶 or 太棒了.
