As others have already pointed out a back up offer just means you are either first, 2nd, 3rd or whatever position in line to buy the home should the current buyer not be able to proceed. This does not mean it's a HUD home and in fact the back up process for HUD homes is different in that the property will show as pending and when a bid is submitted the buyer simply indicates they want their offer to be considered as a backup offer should the initial buyer drop out.
Regardless of if it's a HUD home or not the important concept is that you can wait all you want, you could be willing to subsequently offer better terms or money or have a more favorable timeline but none of that matters unless the current buyer(s) fail to perform in any of 100 different ways from paperwork, to financing to inspection disagreements. to losing a job etc.
Any more, in the in greater Indy market and many markets, it's rare for a property to be pended but rather it will show as active with some sort of status like Inspection, Contract signatures, financing etc. Agent's can eliminate these properties from what you are seeing when they send you listings but they will continue to show as active (which is misleading) on websites like Realtor.com, Trullia and even many agent websites.
I do not encourage my buyers to "get in line" unless you truly have no time constraints because you can invest weeks and months of time without getting the home. It can also be a very frustrating process when you fall in love with home and then can't buy it because you were just too late!
That said if you decide to get in line you want/need to make sure you have a very well written backup offer that provides effective escape clauses should you find another property and want to easily cancel your back up offer with you earnest money intact to move on to the next place.
Good luck with your search. If you have questions feel free to email or call me.