MOSS Question:

Synchronous event are the ones in which the caller needs to pause to wait for a response. The fact that it waits for a response means that the call is a “blocking” call to the event handler. This gives the thread that encountered the event an opportunity avoid executing code that the event identifies undo the effects of code that the event identifies.

Asynchronous event is one in which the caller continues without pausing for a response. This allows concurrency between both the caller and the method being called.