In the case of cryptocurrency Proof-of-stake is a method of securing a network and achieving distributed consensus through requesting users to show ownership of a certain amount of currency.
Term Proof-of-Stake is used when talking about cryptocurrencies. Here is a Wikipedia page 
, however it can be used in a wider sense when talking about blockchain technology used for other purposes than financial transactions.
In even wider sense Proof-of-Stake is related to the notion of commons. You wont be interested, unless you stupid, in damaging something if you own a part of it, and if the safety of the part that you own depends on the safety of the other parts. So if you can show that you are the owner of the part or something you can use it to have a trusted permission to access a whole. It can be a network, a forest with animals, or rabbits on pasture, a company with shares etc.