Code bowling is a competition to solve a particular problem in the most bytes possible. Must be used with other restrictions so that arbitrarily high scores aren't trivially possible.
A code-bowling challenge is a challenge in which a problem must be solved using the most bytes or similar scoring criteria. Making a good code-bowling challenge is difficult, since comments, no-ops and other means can be used to pad programs to an arbitrary length. Some possible ways of preventing this include banning comments or penalizing repeated characters.
In general, code-bowling challenges are not popular because of this dilemma. If you choose to make one, be sure that your challenge is a good fit for code-bowling and that you have taken measures to prevent arbitrary padding of programs.