Homonym wordplay (i.e. peace - piece). Used to project the fact that one can be at peace "in pieces". Used mostly as a valediction, or a way to say goodbye. When one says this word, it sometimes means that they feel their life is in pieces, yet they are at peace.
John: You'll be alright. Just remember you have people that care about you.
Steve: I know. Thanks man. Well I gotta go.
John: Ok buddy. ttyl.