Explanation
In an environment where Salesforce users are enabled to access Google Apps from within Salesforce through App Launcher and Connected App setup, Google is the service provider and Salesforce is the identity provider. A service provider is an application that provides a service to users and relies on an identity provider for authentication3. A connected app is a service provider that integrates an application with Salesforce using APIs4. An identity provider is an application that authenticates users and provides information about them to service providers3. The App Launcher is a feature that allows users to access Salesforce, connected, and on-premises apps from one location5. In this scenario, Google Apps are connected apps that provide services to Salesforce users, such as Gmail, Google Drive, and Google Calendar. Salesforce is the identity provider that authenticates users and allows them to access Google Apps with their Salesforce credentials using single sign-on (SSO)6.
References: Identity Provider Overview, Connected Apps Overview, App Launcher, Single Sign-On for Desktop and Mobile Applications using SAML and OAuth