Carol-Ann Matignon posted her attempt at demystifying the terms CEP, BPM and BRMS here. It is a very interesting post in which she makes an analogy to the human body’s functions as a comparison and a helper to understanding her definitions. That post is worth the read, but I will quote here definitions here:

The CEP / BPM / BRMS world seems fairly simple after all:

• CEP module receives or intercepts a flurry of events and processes them with the objective of figuring out what those events are relevant for; it triggers the appropriate business processes or decision services
• BPM module receives the request for a given process to be applied to a higher level entity (an application, a document…); it automates the steps defined in the business process
• BRMS module is invoked with a given context to apply business rules; it makes a business decision 

Enjoy!