What is Rockyou wordlist?
rockyou wordlist is a password dictionary, the collection of the most used and potential password. Many Password cracking tools are used dictionary attack method, in this case, you will have requirement of password wordlist. so Offensive Security have added already many dictionaries in Kali Linux by default, RockYou wordlist is one of the biggest dictionaries.
Unzip rockyou.txt.gz into rockyou txt
#gzip -d rockyou.txt.gz