SCS is a small cryptographic protocol layered on top of the HTTP cookie facility [RFC6265], that allows its users to produce and consume authenticated and encrypted cookies, as opposed to usual cookies, which are un-authenticated and sent in clear text.
By having a non-tamperable proof of authorship attached, each SCS cookie can always be validated by the originator, making it possible for a server to handle clients' session state without the need to store it locally. In fact, an SCS enabled server could completely delegate the application state storage to the client (e.g. a web browser) and use it, in all respects, as a remote storage device. The result of the cryptographic transformations applied to state data can be used to ensure that its information authenticity and confidentiality attributes are the same as if they were stored privately on server-side.