In computer science, soft state is state which is useful for efficiency, but not essential, as it can be regenerated or replaced if needed.
It is a term that is used for information that times out (goes away) unless refreshed, which allows protocols to recover from errors in certain services.
[1][2] The term was coined by David D. Clark in his description of the Defense Advanced Research Projects Agency (DARPA) internet protocols.
[1] While in general less efficient than well-designed "hard state" protocols when tuned for a particular network regime, soft state protocols behave much better than hard state protocols in an unpredictable network environment such as the Internet.
[3] This computer science article is a stub.