x represents the number of books you have. If you say to a friend "I have more than 25 books" then you can write "x > 25" which says "x is greater than 25"
Something like x = 50 will make x > 25 since 50 is larger than 25. In contrast, a value like x = 20 is going to make x > 25 false because 20 > 25 is false (20 is smaller than 25, not larger)