To understand what you are downloading, it helps to break the term down:

This is a simple text file used to store "environment variables." Developers use these to keep sensitive configuration data—like API keys, database passwords, and port numbers—separate from the actual application code.

In summary, a "Download Env rar" is a package containing vital configuration instructions for a program. While essential for development, they should be handled with the same level of security as a master key or a password.