FBP is a programming paradigm that defines applications as networks of black-box processes, exchanging data across predefiend connections by message passing.
The connections are always specified external to these processes. This allows a product to be thought of as a holistic system just as much as it is a selection of separate services.
The best source for this is probably the google group where the founder of this idea discusses the paradigm. https://en.wikipedia.org/wiki/Flow-based_programming