.UU File Extension
What is a UU file?
File created by uuencode, a Unix program used for converting binary data to text; contains the textual encoding of an original binary file; often used to email a binary file in a text format so that the file does not become corrupted.
"UU," which stands for "Unix to Unix encoding," is most commonly used to transfer files on Unix-based systems. UU files are more often seen with a .UUE extension.
UU files can be decoded back into the original binary file using uudecode.