OAuth is an open standard for access delegation. OAuth provides to clients a "secure delegated access" to server resources on behalf of a resource owner.
Designed specifically to work with HTTP, OAuth essentially allows access tokens to be issued to third-party clients by an authorization server, with the approval of the resource owner. The third party then uses the access token to access the protected resources hosted by the resource server.
More information can be found here
Access token- A token used to access protected resources.Authorizationcode - An intermediary token generated when a user authorizes a client to access protected resources on their behalf. The client receives this token and exchanges it for an access token.Authorizationserver - A server which issues access tokens after successfully authenticating a client and resource owner, and authorizing the request.Client- An application which accesses protected resources on behalf of the resource owner (such as a user). The client could be hosted on a server, desktop, mobile or other device.Grant- A grant is a method of acquiring an access token.Resource server- A server which sits in front of protected resources (for example “tweets”, users’ photos, or personal data) and is capable of accepting and responsing to protected resource requests using access tokens.Resource owner- The user who authorizes an application to access their account. The application’s access to the user’s account is limited to the “scope” of the authorization granted (e.g. read or write access).Scope- A permission.