SharePoint Workflow provides organisations with the ability to create approval processes, document review, archiving, alerting etc around pages, documents or lists.
What is a workflow?
A workflow is series of tasks that each need to be completed to complete a process.
For example, a typical scenario may be a team of consultants working on a proposal document. Once the draft document is complete and added to SharePoint an approval process begins whereby the team leader is alerted that the document is complete and ready for checking. The team leader can then approve or reject the document and provide feedback. On approval the workflow could continue to another approval stage or at this point it may be complete.