A rebound relationship is one where you (or your partner if they're the one rebounding) are still affected by a previous significant relationship. That impacts on either the quality of the current relationship or your perception of it.

In essence, when you're in a rebound relationship you spend a significant amount of time focusing on your previous one. Focusing on what could have been, what went wrong, wondering if you did the right thing in splitting up and lots more besides. All the time you focus on your old relationship you are draining the potential of your current one to be successful.

You spend the time focusing on the old relationship because you have unanswered questions, because you still hurt from some of the experiences you went through, because you haven't taken the time that your mind and your heart needs to work through the painful emotions you're still feeling.