| Application | Your Sinch Application. Manage apps in the Developer Dashboard | 
| Application Instance | One installation of the application on a single device. | 
| Application Key | The key uniquely identifies your Sinch Application. A key looks like d404a4d3-51cf-45e2-bc32-e294ae879d58(lowercase hexadecimal formatted UUID). | 
| Application Secret | A secret used to for authentication and authorization. A secret looks like oYdgGRXoxEuJhGDY2KQ/HQ==(Base64-encoded string representation). | 
| Callee | The user receiving a call. | 
| Caller | The user making a call. | 
| User | An end user. | 
| User ID | Identity of a User in the application domain. | 
| Active Connection | A socket connection for signaling purposes where incoming calls are received. | 
| Web push | Definition needed here |