Definition:
Single Piece Flow is a fundamental element of becoming lean. To think of processing one unit at a time usually sends a shudder through the organisation which has batch manufacturing as its life blood. The word “one” does not necessarily have a literal meaning. It should be related to the customers’ requirements and could be one unit of order. However, what it does mean is that the organisation should only process what the customer wants, in the quantity he wants and when he wants it.
Further Reading:
Book: The Lean Startup by Eric Ries