The .7z format typically uses the LZMA algorithm, which provides superior compression by finding similar patterns across a larger "dictionary" of data. Extraction and Management Does 7z compress better than zip? - Microsoft Community Hub

The file is the third part of a multi-volume 7-Zip compressed archive. In technical terms, it is a split file created to break down a large "solid" archive into smaller, more manageable pieces for easier sharing or storage. Core Technical Concepts

When a file is too large for a specific storage medium or email attachment limit, it is often split into segments. You cannot "open" part .003 on its own. You must have all preceding parts ( .001 and .002 ) in the same folder to successfully extract the data.