The Honeymoon period

I am confused by this statement. What does it mean to be in a honeymoon period? I understand the whole, in love with someone that you don't really get along with. But I have seen people that I thought would never be together in the long run, continue to make choices to stay together. They're obviously no longer in the honeymoon stage. It's just weird, maybe I haven't had a honeymoon stage, or maybe it's that I self protect. I dunno if any of this makes any sense. I need to work.
Peace-
T