What is a BOND?

[Ebahi Ejerekhile]

I've been speaking with an administrator of a property who previously had her property under contract with a different investor. She was told by the investor  that she needed a bond? To protect herself. However she says that the bond fell through and that she hasn't heard from the investor in about two weeks (since the bond fell through).  She is not sure why she got the bond but was told by The investor that she needed it so she tried to get it but is not really sure what it does.  Do an administrators of properties need a bond, and what exactly does it do?  It was her fathers property but no will was left.