PTBNL

From SoSH

Player to be named later (as in trade was made for XXXX for a PTBNL). Trade must be made within six months, and must come from a different league (such as minors or AL vs. NL) than the team he is trade to. Cash considerations (or a free meal) can go instead (usually agreed on before trade) if no acceptable player is found.

If you actually had to look this up, you probably should read a transaction primer such as this one from ESPN's Rob Neyer.