A juz' is a part of the Quran. You know how a big book has many chapters and sections? The Quran is like that too. It has 30 big parts that are called "juz'" in Arabic. Each juz' has smaller chapters inside it called "surahs." So, if you are reading the Quran, you can read one juz' at a time. It helps to keep track of where you are and to break up the big book into smaller pieces. Kind of like eating a big pizza one slice at a time!