Question: what is x divides y?
Answer: Not sure how every single other answer to this managed to get it wrong, but the notation x|y is used to describe the relation “x divides y” Or in other words, x is a factor of y, and y is divisible by x. For instance, 3|15 means that 3 divides 15 because 15=3⋅5, and 3 is a factor of 15.