A relying party (RP) is a computer term used to refer to a server providing access to a secured software application.
Instead of the application authenticating the user directly, the RP can extract these claims from the token and use them for identity related tasks.
[2] The OpenID standard defines a situation whereby a cooperating site can act as an RP, allowing the user to log into multiple sites using one set of credentials.
The user benefits from not having to share their login credentials with multiple sites, and the operators of the cooperating site avoid having to develop their own login mechanism.
[3] An application demonstrating the concept of relying party is software running on mobile devices, which can be used not only for granting user access to software applications, but also for secure building access, without the user having to enter their credentials each time.