Hello @bhavna.lintel
The applicationAPIKey is used to consume DreamFactory APIs. Each app has a unique API key that is sent with each request. When no session token is provided, the request is considered to be from an unauthenticated user and the system uses the API key to look up the default role for the app. The API can be generated in the DreamFactory dashboard.
More information on creating an app and generating API keys can be found here on DreamFactory guide
Let us know if you any more questions