Embedding knowledge creation, capture, and reuse in business processes so that these steps happen routinely as part of normal work
In simplest terms, a work flow is the movement of documents and tasks through a business process. A Work Flow System provides for the automation of a business processes, in whole or part, during which documents, information, or tasks are passed from one participant to another for acting, according to a set of rules.
Workflow technologies help organisations to automate processes. This results in improved efficiency and consistency of processes, reduced process execution time and improved compliance to processes, and enables organisation growth through the ability to execute administrative and compliance processes consistently around the globe. 
Workflow systems allow a sequence of connected steps to be executed by a user. In the context of knowledge management, the workflows are tied to business processes, documents and content. Workflow helps to enable the execution of standard processes and information flows across the organisation. Functionality commonly found in workflow systems includes drag and drop design, digital signatures and approvals, reporting, integration with other knowledge management technologies and the ability to narrate a process with instructions. Additionally, workflows should have the ability to override a step and/or appoint a substitute individual when the person normally responsible for the process is on vacation, away sick or otherwise unavailable. 
- Aligning People, Process and Technology in Knowledge Management by Stephanie Barnes, published by Ark Group, May 2011
Wikipedia on Workflow