Hi Murali!
In short: After certain actions in a Biztalk orchestration the state of the entire orchestration – including full message data, variable values, etcetera – is serialized into xml and stored to the Biztalk database. This is persistence. It’s like a check point in a video game.
Good article: http://blogs.msdn.com/sanket/archive/2006/11/12/understanding-persistence-points-in-biztalk-orchestration.aspx
More good articles: http://www.google.com/search?q=persistence+points+biztalk+2006
//Niklas Häggström – Connecta AB, Sweden