CXD p62 75 数学 题目看不懂

请教CXD数学一题
p62 75

Are there exactly 3 distinct symbols used to create the code words in language Q?

（1）The set of all code words in language Q is the set of all possible distinct horizonal arrangements of one or more symboles, with no repetition.

（2）There are exactly 15 code words in language Q

题目看不懂，请大家帮忙解释一下，谢谢！