SIPOC is a Six Sigma tool; it stands for “Supplier‐Input‐Process‐Output‐Customer”. A SIPOC diagram verifies that process inputs match outputs of the upstream process and that process outputs match the expected inputs of the downstream process.
Source: Guide to the Business Process Management Body of Knowledge – ABPMP BPM CBOK V3.0.
Read this article that shows an example of SIPOC: What is a SIPOC? TQMI UK web site.