It means more than, "I choose not to vote."

It means "I will not participate in the decision at all."
This means that the member with voting rights has a personal Conflict of Interest with the motion and wishes to protect his integrity by not participating in the decision.
A personal Conflict of Interest involves a potential gain which other voting members will not receive from this decision. It does not include such situations as ...

1. "This decision involves a friend's interests, and I don't want to vote against his interests."
   
2. "I am so disgusted with the potential result of this vote that I will show my disapproval by not voting."
   
3. "I am too lazy to prepare before a meeting, and I have no idea what this decision involves."

1. Must not make the motion,
   
2. Must not second the motion,
   
3. Must not debate for the motion,
   
4. Must not debate against the motion,
   
5. Must not vote on the motion.