The question was asked somewhere on Linked In.

For me, 'workflow' is related to the flow of people's work.

A Business Process is larger : in general it will include a workflow (represented by Actors roles and human tasks) except if this business process is fully automatic (which is in practice never the case).

BPM has M for "Management" in it so : How do you manage (Model, Assemble, Monitor, Improve) your processes and in particular your workflows.

See a part of the discussion here :
http://www.codefreez.com/content/workflow-vs-bpm-what-differance