有意思 (yǒu yìsi) is a phrase meaning 'interesting, fun' — it describes something that catches your interest or is enjoyable. It's more general than 好玩儿 (hǎo wánr), which focuses on being 'fun to play/do', and less formal than 有趣 (yǒuqù). The opposite is 没意思 (méi yìsi 'boring').