aura:waiting and aura:donewaiting are System Events in Lightning Framework.

aura:waiting Event :

• This is an application level event.
• This event indicates that the app is waiting for response to a server request.
• This event is fired before aura:doneWaiting.
• This event is automatically fired when a server-side action is added using $A.enqueueAction().
• The aura:waiting event is handled by a client-side controller.
• A component can have only one tag to handle this event.

aura:donewaiting Event :

• This is also an application level event.
• This event indicates that the app is done waiting for response to a server request.
• This event is fired after aura:waiting.
• This event is automatically fired if no more response from the server is expected.
• This event is also handled by a client-side controller.