I'm not sure, and I know others can answer better, but I think they're extra nights received in promotions that are going on at FairField Inn and Courtyard where you can earn a free night after staying 2 nights. They also might be considered bonus nights when you get extra nights with the Marriott charge card.
I see there are other posts on this listed at the side of this post under "More Like This". They can probably answer better.
I went ahead to try to answer so you wouldn't think you were being ignored, because it's often hard for me to answer when I can't find my way back after having to sign in and not being able to find the path used for the conversation.
I think the term "bonus" is used in different ways. Bonus Nights, as far as your Marriott Rewards account is concerned, are nights that come from Credit Card spending, Rollover nights, some Promotions, and Events. They're used to help you attain Silver, Gold, or Platinum thresholds. They also count for Lifetime nights.
|Bonus Nights Earned:||44|
|Rewards Credit Card:||5|