Original project description can be found at: https://github.com/remzi-arpacidusseau/ostep-projects/tree/master/initial-utilities/
From above link: "The type of compression used here is a simple form of compression called run-length encoding (RLE). RLE is quite simple: when you encounter n characters of the same type in a row, the compression tool (wzip) will turn that into the number n and a single instance of the character."
For example, "aaabbbbbcc" becomes "3a5b2c".