'말이야' itself doesn't work, it needs more phrases to make it perfect. meaning also depends on contexts. Chally's explanation can be one of them. originally, '말이야' comes from '말(a word) 이다(BE verb)'. for example, '어 그거 말이야!' (yes, that's what i meant or yes that's what i want or yes that's it) '그게 말이야...........' (somebody's hesitating before doing or saying something, because of being afraid to be blamed or to be told off) '그러게 말이야.' or '내말이 그말이야' (that's what i am saying or tell me about it) '그건 내가 사랑한다는 말이야' A: what do you mean by that? B: I mean, I love you. '그러지 말란 말이야' (i wish you wouldn't do that) it's a stronger expression than ' 그러지마(don't do that)' '내가 말이야...' (tell you what) '우리 데이트 말이야...' A: You stood me up. B: for what? A: our date! (우리 데이트 말이야) B: oh..sorry I totally forgot about it. (in here, it means..what i try to saying is...) so many~:)

when you don't want to describe the object... you can use these sentence I think , it is mean that smilar with "you know what" for ex] when you talk with another person, you use this " you know" between sentences. in other words... 있잖아 is same meaning with 말이야. and we use this " 있잖아 그거 말이야 " when we talk with friend.