A SIPOC diagram is a flowchart (about the highest level possible) that shows the Suppliers, Inputs, Processes, Outputs, and Customers for a given process.
SIPOC diagrams are a great way to quickly understand a process at a high level, ensuring that no major aspects of the process are overlooked.
SIPOC’s are typically followed up with more detailed process maps for a full understanding of the process.
See sipoc.info for more information and templates.