: 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.
The filename suggests it is part of a numbered series (e.g., "04") within a larger collection of data. 04 Knowledge.rar
If you received "04 Knowledge.rar" from the internet or an unknown source, follow these precautions before opening it: Need to open, create, or convert a RAR file? - WinZip 04 Knowledge.rar