What is eCash in ATM?

I've noticed that some ATMs are now advertising the ability to withdraw or deposit eCash. Could you elaborate on what eCash actually is in the context of an ATM? Is it a digital currency that can be accessed through traditional banking systems? If so, how does it work? Does the ATM interface allow users to seamlessly convert between fiat currencies and eCash? Also, what security measures are taken to ensure the safety of these transactions? Understanding the full functionality and implications of eCash in ATMs would be invaluable for those considering its use.