: The .rar extension stands for Roshal Archive . It is a proprietary format used to bundle multiple files into a single, smaller package to save storage space and make sharing easier.
Because Windows and macOS do not always support .rar files natively, you will need a third-party "unarchiver" or "extractor": 04 Knowledge.rar
The filename suggests it is part of a numbered series (e.g., "04") within a larger collection of data. 04 Knowledge.rar