One-to-One Correspondence is a mathematical concept that refers to a relationship between two sets where each element in one set is paired with exactly one element in the other set. This means that no element is left unpaired, and each element is matched uniquely. For example, if you have a set of apples and a set of oranges, a one-to-one correspondence would mean that each apple is matched with one orange. This concept is often used in counting and comparing the sizes of sets. If two sets have a one-to-one correspondence, they are considered to have the same number of elements. For instance, if you can pair every student in a class with a desk without any leftover, then the number of students is equal to the number of desks.