It is a RAR (Roshal Archive) file, specifically a "split" or "spanned" volume. This means the original data was too large for a single file and was divided into multiple parts (e.g., part01, part02... part21).
Unless you are certain of the source and intentionally downloading a multi-part archive, avoid downloading or extracting this file. Gh0stb.part21.rar
If a hash (MD5/SHA-256) was provided by the original source, verify it to ensure the file hasn't been tampered with or replaced by a malicious version. It is a RAR (Roshal Archive) file, specifically
It is often found in repositories containing leaked databases or "combolists" (collections of usernames and passwords). These are used by bad actors for credential stuffing attacks. Gh0stb.part21.rar