A few days after you ask a question you will receive a request from Yedda to say if the posted answers are good enough, or would you like Yedda to continue actively searching for more people to answer your question.
If you indicate that the answers are good enough, it will be marked as resolved.
If you request that Yedda continues to search for the right people, the question will stay open and Yedda will continue to actively seek people to answer the question.
If you don't say anything, then your question stays open, but it doesn't get actively freshened up anymore. This means that people who run into your question will still see it as open, but Yedda stop searching for people to answer it and does not send any more invitations to people to answer this question.